Sarah is a blue-loving mage who cares little for other kinds of magic and prefers to simply burn stuff to the ground.
She has the lowest possible starting Affection towards the Protagonist (middle finger).
She first encounters the player in Drape's classroom, where she asks to join the Protagonist's party. Allowing her to do so causes Drape to injure her as she's disturbing class.
Depending on when you went to Drape's class, you might have to attend 2 more classes before she'll show up and ask for a heal. Saying you know a healing spell and then using Boost on her both affects her Affection. Ignoring her causes her to run after you in the street, but she'll be pissed at you. You can also use Suppress to make her your slave at this point.
She currently has 7 spells, of which 1 is hidden.
Dating Sarah
With 50 or more affection, it's possible to date her, making her the first datable character added in the game.
To do so, you must play as Dan and have no other girlfriend prior. Once she has 50 affection, you can speak to her in the street and agree to go out with her.
Sarah's past
In the past, Sarah didn't live in the city. However, she was forced to move there when a monster killed her parents, leaving her an orphan. Beliving her parents to have abandoned her, she resents them until proven otherwise during a date with the Protagonist.
While she's a former best friend of Cassandra's, Cassandra fell in love with Sarah (something Sarah is not aware of). Due to Sarah being straight, Cassandra bullies Sarah in hope of not feeling anything for Sarah anymore.
Sarah the Doll
After obtaining the Stone Skin spell, talk to Sarah in the street without her being your slave. Say you're not busy and follow the conversation until she says 'Like plastic, for example?'.
Use Stone Skin on her at this point and she'll remark her skin is like plastic. This also causes her to get a great boost in Affection.
Next time you meet her, agree to turn her into a Doll again but don't change her back. She'll now stand in your room until you decide to fix her and change her back to normal.
While you change her back to normal, it's possible to enslave her.
Slave outfits
Normal
She's wearing a blue dress and swears once in a while, though it's rare.
Mindless
She only says a few words and her eyes are blank, wearing the same outfit.
Eager to Please
Her outfit turns red and she'll do everything she can to make the Protagonist happy.
Tough
She has her blue outfit but a more fearless view on things.