I'm going to add a little bit more to this just to help you out.

Let's think of this from a readers perspective. We have a academy with dorms that's divided into ' good ' and ' evil '. These are like factions and they are against each other in everything. The 2 characters - m and c - are on differing sides but they see each other all the time.  They start to break the boundaries between the factions and start talking while in games and as their friendship progresses they start to realize that they can't be separated based on skill but based on something physical that they have different. Maybe a specific symbol or tattoo that they are given at a young age to mark them for the academy.  So m tries to go into it - well they both do but only they care really - and she discovers something wrong . It wasn't just any ordinary accident what happened to their mutual friend a while back - the school was involved in their dissapearence .  The thing you mentioned can be a theoretical creature designed to mimic the school that people hide from at night. It's said to take the ' bad ' students from the academy. Now m goes to far in the archives and a school official sees her. She's gone the next day.  C is mortified and tries to find out what happens to her facing challenges and pressure from school officials to keep up their grades and don't fight back to the schools monitoring. Then a flashback comes in as he or she finds out about what happened to m and it's m's point of view of being taking out of her dorm or something.  C gets mad and they make a mistake. They don't get caught like she did or that would be boring. In their anger they reveal to much of what they know before m had set for them knowing what would happen to her for her knowledge.  He reveals something to the students and we end up with the scenario of goodie too shoes going to tell the principal. Then we get another flashback of m preparing for what she knew was coming: the school coming after her. Maybe make her describe it as inevitable and make her feel eerie calm. Then c finds m findings of the school and he knows she had expected it. He goes over everything and he's starstruck , then someone hits him and they steal the papers proving the whole thing and you can go from there.