Carton

From Mimi's side (the one drawn on paper:

A normal 17-year-old girl called Mimi in high school until you find out her one secret- she's a magical girl! 

She hates her real self and gets bullied at school but when she's the magical girl 'Moon Jelly', and only then, can she be happy and express herself. Mimi is quite the gloomy girl outside of the costume, in it she's all smiles. It's everything to her.

The magical girls Moon Jelly and Sunny Shark are a duo. Mimi adores Sunny and they're quite dependent on one another, however they don't know each others' real identities.

When she finds out that Sunny is actually her main bully, Mimi breaks down and begins to blackmail Lyrene, Sunny, so that she'll never leave her. 

A very toxic relationship ensues.

From Lyrene's side:

Lyrene is a 17-year-old girl in high school. She's a bad person, relentlessly bullying a girl in her class. Despite that, she somehow becomes a magical girl who protects the world, alongside the other magical girl Moon Jelly.

Her identity as Sunny becomes a sort of mask, with it she can pretend that she's a good person who does no harm.

She becomes extremely close to Jelly, she comes to depend on her for this feeling of elation, of redemption- of everything she's been missing. Being with her makes her whole.

When they finally decide to reveal their identities and Lyrene comes to face with Mimi, the girl who she bullies, her world view shatters. She wants, no, needs to leave. Mimi begins to blackmail her with the threat of exposing her identity just so that she won't leave and strangely enough the idea of someone wanting her that bad is even better than what their relationship used to be. Even so, it starts to take its toll on her, Lyrene becomes more withdrawn and people at school begin to notice just how much more cruel she's being towards Mimi. Mimi doesn't mind, it means that Lyrenes attention is wholly on her.