An unknown individual is out to target the Protagonist, by targeting him/her with Ink Bombs.
Why? Let's find out!
If it doesn't interest you, here's a link to the other routes in the game.
Note that this is just a general outline for the route. It is not a walkthrough.
Mysterious Pranks
As the Protagonist leaves his/her house, a bucket drops down next to him/her out of the blue. The Protagonist is surprised at it and finds a note, saying that it's only the start of that persons revenge.
The Protagonist decides to keep an eye out for more pranks.
Shortly after, the Protagonist's mail box is filled with mails. Each of them seems to have a small lump inside of them. If the Protagonist decides to open them, the letter will get stained with some blue ink, implying that the Ink Bomb was turned the wrong way.
Otherwise, if the Protagonist decides to dispose of them in order not to take any risks, the Protagonist remarks that it was weird.
The next prank happens at the lake. The Protagonist finds a sign with a rope next to it - the sign tells the Protagonist to pull the rope. If done, a bucket falls down on a person who is implied to be the one who set it up, who then hurries off.
Otherwise, the Protagonist hears "what sounds like a female voice cursing [the Protagonist]".
The Shop
In the Item Shop, the Protagonist runs into a mysterious person who is supposedly purchasing a large amount of Ink Bombs - and has been purchasing quite a lot of them lately.
The person instantly tells the shop keeper off, saying that she's paying for them, isn't [she]?
The shop keeper explains that they're not exactly hurting for her business, causing the person to say that she's only after one item, but they apparently can't sell her that.
When trying to explain that it doesn't quite work like that - they have to make a whole new potion and such, the person remarks "Wait until [she] gets [her] bo-" but is cut off at the Protagonist entering the store and instead hurries off without saying anything further.
Target for Revenge: Cassandra
At the School, Cassandra is visibly irritated at someone targeting her with weird pranks.
The Protagonist can either admit to it happening to him/her, too, causing Cassandra to say that they need to put a stop to it. The Protagonist asks if she has an idea, to which she says she does, but then hurries off in order not to rouse suspicion.
Otherwise, the Protagonist can remark that it sucks for her, causing her to bluntly say she's aware of this fact and leaves in order to find out who's behind it all.
Finding the Culprit
After the scene with Cassandra, the Protagonist heads to the small forest next to the Lake. You must reach at least floor 16 to unlock this scene.
Cassandra will be hiding here and tells the Protagonist to hide as well. The Protagonist can either ask what Cassandra is doing or simply agree to hide.
Regardless of choice, an unknown tanned woman soon gets caught in the trap and turns towards the Protagonist and Cassandra and starts scolding the two of them right at once.
You can either ask her what she's doing and why or you can just go ahead and enslave her.
If you ask her, she'll explain that her name is Reese and that she was swimming when Cassandra threw a bottle into the lake, causing her to change gender. She spent quite some time diving in order to get all the shards from the bottle out of the bottom of the lake so no one would get hurt.
When told that Reese could simply have bought a gender change potion, she explains it's not that easy - the one in the lake was so diluted that there was no way to fix it by normal means.
If the Protagonist has the Contract, you can have Reese sign it at this point. Reese will say that she'll think of something for the Protagonist to do later, to which the Protagonist has no objection.
If the Protagonist has the Mysterious Book, it can be given to Reese as well. Reese will then read it and become the Protagonist's slave as a result of the book.
Otherwise, the Protagonist can just use Boost to change Reese's gender back to male. Well, mostly normal.
Finally, you could simply enslave her with the help of Cassandra, causing you to get another slave.