The game can be fairly non-linear at points, and some events are entirely independent of others, so it is fairly difficult to really make a walkthrough to cover everything. I am going to try my best to cover major paths, and how to reach specific special events or splash images.
There will probably be a lot of spoilers, so if you don't want to have the game spoiled, try to be careful about reading paths you have not yet played.
There will probably be a lot of spoilers, so if you don't want to have the game spoiled, try to be careful about reading paths you have not yet played.
Do note that this walkthrough is for 0.21, and may not be complete for later versions. If there is any information missing that you would like me to add, leave a comment with a question and I will answer it and try to add it to the walkthrough.
Heroic Plotline:
This plotline is revolves around the Main Character attempting to use their powers for good. As you are not drawing attention to yourself by building a Harem, Mr. Drape will begin his plan to turn the school's student body into his idea of perfect students, starting with your friend, Val.
To get on this plot line, you will need to avoid making any character your slave. This does not mean you cannot use your magic on other students, strictly speaking, but you will need to avoid outright enslaving anyone, or using spells that will leave a permanent effect on a character.
In the tutorial, most of your choices just influence Val's opinion of you. The major decisions you need to watch out for are after obtaining your magic; you can choose to test your magic on her, or on a monster. Using your magic on Val will subsequently lead to a choice on whether or not to keep her under your control. Choosing to keep her will lock you out of this plot line!
Once you return from the Dungeon, you will be free to roam the school and trigger most scenes in any order. You should visit the Mr. Drape's room to get Sarah to join your party, and Jane's room to get permission to enter the dungeon. You can enter Dr. Tiff's room at any time, but you might as well do it now to get it out of the way for later.
If you talk to Val in the hallway, you have a chance to enslave her, but that will lock you out of the plotline. Trying to enslave her, and failing will instead have Val leave your party but will not lock you out.
The next major plot point of this plot line starts when you have reached the Fourth Floor of the dungeon. At this point, a new conversation with Val will become available. She is now dressed almost exactly like Mr. Drape, and insists that it was her idea. The next conversation takes place in Dr. Tiff's room, where you can report Val's condition to her.
Jane will then meet you in the hallway outside of Dr. Tiff's room appearing to know a little too much about Val's condition. She offers to help, and will wait for you in her room. After accepting Jane's offer, you will need to make sure Sarah is in your active party, and visit Val in Dr. Tiff's room in order to enter Val's mind.
The first floor of Val's mind is meant to vaguely resemble a roller skating rink, and is populated by sentient Roller Blades. Find the pulsating Sigil to go to the next floor. The second floor vaguely resembles a diner, and if you attempted and failed to enslave Val a new enemy resembling a broken heart will appear in battles now. Find the pulsating Sigil to reach the inner-most part of Val's mind and fight the boss guarding it.
Once you have defeated the boss, you will be instructed to cast a long-lasting spell in order to bind Val's soul to your magic, and prevent Mr. Drape's magic from being able to bind to her again. You have several choices at this point:
Suppression: This will enslave Val, and result in your path changing from the Heroic path to the Tempted Hero path. (No scenes have been made for this path yet)
Confusion: This will permanently bimbofy Val. She will not count as your slave, but will move you to the Tempted Hero Path.
Grapple: This will permanently turn Val into her Goth personality, and give her a sudden, new interest in bondage. She will not count as your slave, but will move you to the Tempted hero path.
Charm: This will amplify Val's feelings for the main character, and make her permanently in love with your character, regardless of your other romantic interests. She will not count as your slave here either, but will put you on the Tempted hero path.
Boost: Boost can improve the body in any way, which the main character normally uses for healing. If used here, you will make an imperceivable change to Val's body in order to bind her soul without side-effects.
Once you have left Val's mind, you need to enter Dr. Tiff's room one more time to check Val out from her care. You can put Val back into your party in your room after this scene concludes.
In Ms. Rack's class, there is a scene where you tell her about what Mr. Drape did to Val, which leads to her promising to have a talk with Mr. Drape about not using his power on her.
Once you have reached the 7th floor, a new scene will appear in the hallway with Sarah, who is acting oddly. Apparently, Mr. Drape is not done messing with his students. Take her directly to Jane's room, where she will keep an eye on Sarah while you get a party together. Once you are ready, talk to Jane again to begin the dive into Sarah's mind.
The first floor is fairly straight foward, you need only enter the building to the north. The second floor shows the layout of a building made of fire. You will find Sarah hiding in the lower right room, and will face the boss soon after.
Once the boss is defeated, you have a choice once again to cast a spell on Sarah to affect her personality. If you want to stay on the Heroic path, you should choose to cast Boost on her, which will also improve her Max HP by 50 points.
The other spells that can affect her at this time are:
Confusion: This spell will make Sarah less willing to think for herself, and cause her to develop her Needy personality. She will not count as your slave, but will put you on the Tempted Hero Path.
Charm: This spell will cause Sarah to fall in love with you. She will not count as your slave, but will put you on the Tempted Hero Path.
Suppression: This spell will cause Sarah to become your slave.
Grapple: This spell will bind Sarah's will to yours, and cause her to develop her Tough personality. She will not count as your slave, but will put you on the Tempted Hero Path.
After having seen what you can do to Val, Sarah will try to object to you casting spells other than Boost, but will ultimately be powerless against the spell of your choice. Speak to Jane one last time to get Sarah back into your party, and an offer for her to train you. If you used Boost both times, she will seem somewhat disappointed with you in this exchange.
Talk to Jane once more in her room to initiate your training. Here, you will meet your new training partner, Molly. If you have been good so far, you will have the choice of objecting to using your powers on her, which will lead to Molly joining your party at the end of the scene. If you have been altering the personalities of your friends, or if you have taken any slaves, you will get a different version of the scene that will lead you towards the Tempted Hero path.
Once you have learned the Charm Spell, by casting debilitating magic in combat you will unlock the second of Jane's private lessons. This one covering the usage of the Charm spell. Molly will be helping you again here, and will again be returned to normal afterwards.
Tempted Hero Path:
This path is for those heroes who just couldn't quite behave themselves. The first entry point so far is to follow the Heroic Path without enslaving anybody outright until you have begun the plot to save Sarah's mind. (This means no enslaving Val in her mind) If you alter either girls personalities, charm them, or enslave another character after Sarah has begun showing signs of Mr. Drape's control, Jane's first private lesson will be a bit different and will not result in Molly joining your party.
After you have learned the charm spell, by castinig debilitating magic in combat, you will unlock the second of Jane's private lessons. This one covers using the Charm spell, and Molly will join your party at this point instead.
In Ms. Rack's class, there is a scene where you tell her about what Mr. Drape did to Val, which leads to her promising to have a talk with Mr. Drape about not using his power on her.
Once you have reached the 7th floor, a new scene will appear in the hallway with Sarah, who is acting oddly. Apparently, Mr. Drape is not done messing with his students. Take her directly to Jane's room, where she will keep an eye on Sarah while you get a party together. Once you are ready, talk to Jane again to begin the dive into Sarah's mind.
The first floor is fairly straight foward, you need only enter the building to the north. The second floor shows the layout of a building made of fire. You will find Sarah hiding in the lower right room, and will face the boss soon after.
Once the boss is defeated, you have a choice once again to cast a spell on Sarah to affect her personality. If you want to stay on the Heroic path, you should choose to cast Boost on her, which will also improve her Max HP by 50 points.
The other spells that can affect her at this time are:
Confusion: This spell will make Sarah less willing to think for herself, and cause her to develop her Needy personality. She will not count as your slave, but will put you on the Tempted Hero Path.
Charm: This spell will cause Sarah to fall in love with you. She will not count as your slave, but will put you on the Tempted Hero Path.
Suppression: This spell will cause Sarah to become your slave.
Grapple: This spell will bind Sarah's will to yours, and cause her to develop her Tough personality. She will not count as your slave, but will put you on the Tempted Hero Path.
After having seen what you can do to Val, Sarah will try to object to you casting spells other than Boost, but will ultimately be powerless against the spell of your choice. Speak to Jane one last time to get Sarah back into your party, and an offer for her to train you. If you used Boost both times, she will seem somewhat disappointed with you in this exchange.
Talk to Jane once more in her room to initiate your training. Here, you will meet your new training partner, Molly. If you have been good so far, you will have the choice of objecting to using your powers on her, which will lead to Molly joining your party at the end of the scene. If you have been altering the personalities of your friends, or if you have taken any slaves, you will get a different version of the scene that will lead you towards the Tempted Hero path.
Once you have learned the Charm Spell, by casting debilitating magic in combat you will unlock the second of Jane's private lessons. This one covering the usage of the Charm spell. Molly will be helping you again here, and will again be returned to normal afterwards.
Tempted Hero Path:
This path is for those heroes who just couldn't quite behave themselves. The first entry point so far is to follow the Heroic Path without enslaving anybody outright until you have begun the plot to save Sarah's mind. (This means no enslaving Val in her mind) If you alter either girls personalities, charm them, or enslave another character after Sarah has begun showing signs of Mr. Drape's control, Jane's first private lesson will be a bit different and will not result in Molly joining your party.
After you have learned the charm spell, by castinig debilitating magic in combat, you will unlock the second of Jane's private lessons. This one covers using the Charm spell, and Molly will join your party at this point instead.
Faculty Control Path:
The first thing you need for this path is to enslave Val. You can do this by choosing to test your magic on her, continue casting on her after she warns you to stop, and then keeping her. Alternatively, you can enslave her when she talks to you at the school by casting Confusion, then Suppression on her.
If you enslave Sarah prior to reaching the first note, you can also Enslave Val by having Sarah in her "Eager to Please" form when you touch the note. In the cutscene that follows, you can cast Confusion, then Suppression on her to break her will.
Go into the dungeon, and explore a bit. Find the note on the Third Floor, and attend the first Secret Class with Ms. Rack. Once you have finished, you can enter the library to the right of the dungeon to meet Julia. Do not enslave her. You can make any choices in this conversation you like; you will either agree to help her, or leave the possibility of helping her open.
Once Val has reached lvl 4, you can return to the school and enter Ms. Rack's room where there will be a scene in which she will ask you about Val's odd behavior. You can tell her the truth, or lie to her. This decision will have an impact on her opinion of you, but neither choice will prevent you from enslaving her.
If you have not already, your next target should be to find the second note, located in the top left room of the Fifth Floor. Julia will not allow you to play with her yet, but after giving this note to her, she will allow you to play with your other slaves, and she will tell you Ms. Rack's weakness.
When you return to your room, talking to Val will give you a choice on whether to give her the plan, or wait. If you have not yet made her into the personality you want her to be during the next scene, this is your last chance to change her. If you do, you will need to talk to Julia again and get the intel again. This is a bug that I can't seem to get fixed, so eventually this will change so you can just talk to Val immediately afterward once I do have it fixed. When you tell her the plan, the next time you talk to her will trigger the scene with Ms. Rack.
Important decisions:
There are a couple ways to fail this scene and end up Ms. Rack's slave. If you want to avoid them; or deliberately seek them out they are:
1: Have Val be in her normal personality and tell Ms. Rack to have a make-out fight with her. Val's hesitance to make out with her Aunt will lead to her failing the "battle" and Ms. Rack turning her against you.
2: Have Val be in her Bimbo personality, and tell Ms. Rack to have a make-out fight with you. Val's bimbo form is unreliable, and she ends up spiking both of your drinks, causing you to be too tipsy to resist Ms. Rack's power.
Getting Dr. Tiff
You will need to follow the Student Control Path until you have at least 3 slaves, and have attended the second of Jane's lessons to continue this path. Once this is done, Val will confront you on the streets to reveal that she has been cured of your control by Dr. Tiff! She doesn't trust you enough to talk for long; but asks you to consider giving up your slaves freely. You can talk to Dr. Tiff at this point to surrender slaves, which will lead to the start of the Redemption storyline.
Otherwise, pay Julia a Visit. If she is your slave, or if you have given her enough notes, she will have some info on Dr. Tiff now. Once you have this info, you can either visit Ms. Rack, or if she is your slave and knows her first Assistive Spell, Cassandra, to begin planning your enslavement of Dr. Tiff. Once you have talked to one of the two characters, head to Dr. Tiff's room to enslave her.
You will be able to talk to Val in the hall again after Dr. Tiff is enslaved; she saw you in her room and is hopeful that you've decided to give up your slaves. You can lie to her and tell her that you have; or you can tell her that Dr. Tiff is your slave now too. You can let this scene play out on it's own, or at any time you can cast confusion on her to get her to agree to come back to your house. Once there, you can talk her back into a trance in one of two ways based on your choice.
Getting Dr. Tiff
You will need to follow the Student Control Path until you have at least 3 slaves, and have attended the second of Jane's lessons to continue this path. Once this is done, Val will confront you on the streets to reveal that she has been cured of your control by Dr. Tiff! She doesn't trust you enough to talk for long; but asks you to consider giving up your slaves freely. You can talk to Dr. Tiff at this point to surrender slaves, which will lead to the start of the Redemption storyline.
Otherwise, pay Julia a Visit. If she is your slave, or if you have given her enough notes, she will have some info on Dr. Tiff now. Once you have this info, you can either visit Ms. Rack, or if she is your slave and knows her first Assistive Spell, Cassandra, to begin planning your enslavement of Dr. Tiff. Once you have talked to one of the two characters, head to Dr. Tiff's room to enslave her.
You will be able to talk to Val in the hall again after Dr. Tiff is enslaved; she saw you in her room and is hopeful that you've decided to give up your slaves. You can lie to her and tell her that you have; or you can tell her that Dr. Tiff is your slave now too. You can let this scene play out on it's own, or at any time you can cast confusion on her to get her to agree to come back to your house. Once there, you can talk her back into a trance in one of two ways based on your choice.
Student Control Path
This path begins when you have enslaved at least 2 characters, and have not started the Heroic Path. When you visit Jane, she will confront you about your use of your powers on other students.
She is not angry with you, however. For some reason, she wants you to keep using your powers; just a little more discreetly. She even offers to help you hone your powers for purposes that the stuck-up Mr. Drape would never allow.
Once you have a third slave, a new scene will be available. Jane will introduce you to your new training partner, Molly, who has volunteered to allow you to cast your magic on her for extra credit in Jane's class. You will not be able to keep Molly once she is enslaved, but she will be back for more as you learn new spells.
Once you have learned the Charm Spell, by casting debilitating magic in combat you will unlock the second of Jane's private lessons. This one covering the usage of the Charm spell. Molly will be helping you again here, but will not join your party and will be returned to normal afterwards.
Once you have a third slave, a new scene will be available. Jane will introduce you to your new training partner, Molly, who has volunteered to allow you to cast your magic on her for extra credit in Jane's class. You will not be able to keep Molly once she is enslaved, but she will be back for more as you learn new spells.
Once you have learned the Charm Spell, by casting debilitating magic in combat you will unlock the second of Jane's private lessons. This one covering the usage of the Charm spell. Molly will be helping you again here, but will not join your party and will be returned to normal afterwards.
Individual Enslavements
Val:
1: During your first trip into the dungeon, if you test your magic on her, and keep going at every prompting she will become your slave.
2: During your first random conversation with Val in the school, you can cast Confusion on her, then Suppression to enslave her. If you do not cast Confusion, she will leave your party.
3: If you have Sarah enslaved and in her Needy form, and both Sarah and Val in your party at the time, Val will notice and question her behavior. You can enslave Val by casting confusion, then suppression in this conversation.
Sarah:
In order to meet Sarah, you need to attend Mr. Drape's first class.
1: After attending Mr. Drape's class, and Dr. Tiff's class, Sarah will appear in the hallway, still affected by Mr. Drape's curse. She's twisted her ankle trying to walk without using her arms for balance, and needs someone to help her out. You can either use suppression at any time to force her under your control, or you can offer to heal her, then cast suppression instead of boost for a different scene.
2: If you refuse to heal Sarah in the hallway, she will come after you on the streets. During this conversation, if you have enslaved Val already, you can enslave her at any time, or you can goad her into attacking you first for a different scene. If Val is not your slave, she will stop you from enslaving her.
3: If you have Val enslaved and in her slave form, and both Sarah and Val in your party at the time, Sarah questions Val's behavior. You can choose to either admit to putting Val under your control which will cause Sarah to challenge you to enslave her to prove that you are lying, or you can cast confusion, then suppression on her at any time.
4: After waking Sarah up from being an inanimate doll during the special doll plot-line, you can cast suppression on her to enslave her.
4: After waking Sarah up from being an inanimate doll during the special doll plot-line, you can cast suppression on her to enslave her.
Julia:
1: After you have attended your first secret class, Julia appears in the library. When talking to her for the first time, at any time you can use the confusion spell on her, followed by Suppression to make her your slave.
2: In the same scene as above, after you have confused her, you can instead cast Grapple on her when she tries to leave for a splash image an alternate enslavement sequence.
3: See alternate Berserker Recruitment
2: In the same scene as above, after you have confused her, you can instead cast Grapple on her when she tries to leave for a splash image an alternate enslavement sequence.
3: See alternate Berserker Recruitment
Ms. Rack:
See faculty control path
Cassandra:
In order to meet Cassandra, you need to upset her. You can accomplish this by either being friends with free-willed Sarah, and standing up for her during one of her conversations when Cassandra shows up to make fun of her, or by making Julia into a fanatic and agreeing with her when she makes the claim that you are stronger than Cassandra.
1: Cassandra will challenge you to meet her in the Dungeon for a duel the first time you talk alone. When you go there, she will offer to join your party if you pretend that you lost. Refuse the offer and duel her. During the duel, cast Boost on her instead of attacking her.
After casting Boost a few times, the battle will end, and you will get to choose what kind of cow you prefer her to be in her cow form. Cassandra will demand to be changed back immediately, and you are given the option to leave her as she is, or return her to normal. Choose to return her to normal, then cast Suppression instead to enslave her.
Slave Chatter:
There are several scenes that will play out at random in your bedroom if you have the right conditions met. These are the conditions:
1: You need to have enslaved Cassandra and have her in her Cow form, and you need to have enslaved Sarah and have her in her Tough form.
2: You need to have Val, Sarah, and Cassandra enslaved, and all in their normal personalities.
3: You need to have enslaved Cassandra and have her in her Maid form, and you need to have enslaved Val and have her in her Bimbo form.
4: You need to have Sarah enslaved and in her Needy form, and you need to have Julia enslaved and in her Fanatic form.
5: You need to have Cassandra and Julia enslaved, and both in their Normal forms.
Special Sequences/Features
Doll Sarah: Sarah will approach you, wanting you to turn her into a doll. If you accept, you can change her permanently into a living doll.
Requirements:
1: Sarah must have 25 affection for you. Affection is an invisible stat that tracks how much a character likes you based on your interactions with them. In order to build up enough affection, here are some things that can boost her affection.
- + 10 Telling her that you will heal her when she comes to you for help in the hall.
- + 10 Casting boost on her in that conversation when she is in the hall.
- + 10 Telling her you don't mind being broke.
- + 15 Waiting to see what happens when Cassandra is antagonizing Sarah.
- + 20 Casting stone skin on her when she mentions plastic during the scene where she asks about the stone skin spell.
3: Must know the Stone Skin Spell.
4: When Sarah comes to you about the Stone Skin spell, wait until she mentions plastic before you cast the Stone Skin spell on her.
5: You must attend the first of Jane's private lessons, on any path.
Once these requirements are all met, Sarah's chat icon will appear on the streets. She has been thinking a lot about having plastic skin, and wants more. If you accept her offer, she will come with you to your room where she will strip and allow you to cast the spell on her.
Once transformed, she becomes completely inanimate and leaves the party as a result. During this scene you can cast Boost on her to give her the ability to move and think once more. If you allow the scene to end she will decorate the corner of your room, and you will be able to "talk" to her at any time for a close up look at her and another opportunity to cast Boost.
There are a few variations of the scene at this point; if you leave her in your room, you will get one of three different endings to the scene depending on how many levels you gained since leaving her there. Additionally, you can enslave her after waking her by casting Suppression.
Recruiting Berserker
There is a 1/20 chance when entering Dr. Tiff's room that there will be some students complaining about vampire attacks on the first floor. This scene is not necessary to meeting the berserker, but will have a 100% chance of occurring once you have seen the berserker once, and is a sort of in-game clue that something worth looking out for is on that floor.
On the first floor of the dungeon after you have reached lvl 3, when a random encounter would normally occur on other floors, there will be a chance that the Berserker will attack the party. This chance starts off very low, and increases the higher level you get.
The Berserker will run away when injured, rather than fighting to the death like most monsters. If you cast Suppression on her several times, however, she will slowly calm down and become reluctantly docile. Talk to her in your room in order to learn that she really wants to join your party so she can fight more.
Go to the library next, and talk to Julia. If you have not yet given her any of the notes she is looking for, she will be reluctant at first but will agree to help after seeing the Berserker in person. She will offer to teach the Berserker to behave herself well enough to join you in the dungeon for apparently no cost to you.
Once you have left the Berserker in Julia's care, you can talk to her on the streets next. She will tell you her name is Ashley and that Julia has given her permission to join you. She can be added to your party now in your bedroom like any other party member.
*************Alternate Path*************
There is an alternate path to recruiting the Berserker. In this path, once you learn about the berserker you should visit Julia right away. She will ask to join you on your search of the first floor, but will not join your party. This time when you encounter the Berserker, Julia tries to reason with her, but fails. The fight begins and you can use Suppression on her as before to put her under your control.
If you defeat the Berserker via damage, a scene will play out where Julia suggests slowing her down, but does not want you to use Suppression. You can either let the conversation play out, cast Boost to heal Julia, or cast Suppression to enslave her before continuing on to catch the Berserker.
Once the Berserker is under your control, return to the library where Julia will offer to help her restore her humanity, then speak to the Berserker on the Street to have her join your party.
********************************
Once you have reached the 10th floor of the dungeon, the next sequence will be available in the Library while Julia is in her normal personality. Talk to Julia to trigger a scene with her tutoring Ashley. Your decision in this scene affects Julia's opinion of you but does not affect the plot.
Talk to her again to trigger a new scene where Ashley has gone missing. This will cause Ashley to be removed from your party. If Julia is your slave, she will admit to sending Ashley away. If she is not, she will admit it more reluctantly. For her disobedience, you have a choice to either punish her or not.
Return to your bedroom, where Ashley is waiting. If you chose to punish Julia, there will be a sequence where you enslave Ashley; breaking her mind in the process. After that, the main character will make a chance to Julia's mind, enslaving her if she hasn't been enslaved already and ensuring she will always be aware of her betrayal and her punishment for it.
If you choose not to punish Julia, you will find Ashley at your room, and she will return to your party without conflict.
Item Store:
The item store will become available once you have attended the second of Jane's private lessons. You will find Molly there volunteering as a store clerk, and upon learning that your family is too poor to afford a crystalizer gives you hers. At this point, you will be able to collect Gems in the dungeon.
Shopping at the store can influence Molly's opinion of you. Buying Love and Trust potions will cause her to dislike you, while Roses and Ink Bombs make her like you more.
Willing Slave Cassandra:
If you transform Cassandra into a cow, but do not enslave her, a sequence of scenes will become available involving Cassandra dealing with her new cow form in the school hallway. During these scenes, Cassandra will become increasingly desperate for you to change her back. The furthest into the dungeon you will need to go for these scenes will be the 7th floor.
When you have the choice between refusing to help her or making a deal, refuse to help her. Then, when she attempts to guess at what you want in the next scene you will have the choice between agreeing with her or correcting her. You should correct her.
The final scene in the sequence takes place in the bedroom, where you can make one of three choices; you can tell her she's been punished enough, ask her to join your party, or willingly become your slave. The first two give you the option of either restoring her to normal or enslaving her afterwards anyway, while the last one has her agree to become your slave willingly.
Sarah's Home, Bubble Spell, and Possession Spell:
This major sub-plot has several requirements. You must have 50 affection with Sarah, and have reached the 10th floor or lower; but not further than the 15th floor. You also need to have seen Sarah mention her past during your play through. This occurs at three different points, such as if you leave her inanimate for a while, or have an ending during the first date that results in her saying that she needs to get back to her housing. Finally, if she is your slave, she will also need to have her normal personality.
If you go to the lake once the conditions are met, you can talk to Sarah to trigger a scene in which she asks you to accompany her to her old home. If you refuse, this leads to an alternate plotline where she is found injured by an explorer. If you agree to go, a lengthy scene will play out, including an unwinnable battle.
After the battle, the scene will continue until Sarah enters a trance and casts the Bubble spell. At this point, Sarah will have access to the bubble spell in combat. Once you return home, it is revealed that the ghost of Sarah's mom had possessed her. You can enslave the ghost of Sarah's mom with the Suppression spell. If you do so, it will unlock the Possession Spell.
Sarah's Home, Bubble Spell, and Possession Spell:
This major sub-plot has several requirements. You must have 50 affection with Sarah, and have reached the 10th floor or lower; but not further than the 15th floor. You also need to have seen Sarah mention her past during your play through. This occurs at three different points, such as if you leave her inanimate for a while, or have an ending during the first date that results in her saying that she needs to get back to her housing. Finally, if she is your slave, she will also need to have her normal personality.
If you go to the lake once the conditions are met, you can talk to Sarah to trigger a scene in which she asks you to accompany her to her old home. If you refuse, this leads to an alternate plotline where she is found injured by an explorer. If you agree to go, a lengthy scene will play out, including an unwinnable battle.
After the battle, the scene will continue until Sarah enters a trance and casts the Bubble spell. At this point, Sarah will have access to the bubble spell in combat. Once you return home, it is revealed that the ghost of Sarah's mom had possessed her. You can enslave the ghost of Sarah's mom with the Suppression spell. If you do so, it will unlock the Possession Spell.