Leviathan

Leviathan or Levi, for short, is a Heretic who is a member of the Four Beast, a small group of Heretic's with unknown goals. Before becoming a Heretic, Levi was once a mass-produced Nikke who used to work for the Ark. However, after becoming exposed to a black liquid called Dark Matter, it stuck to her body, making her appearance that of a slime monster, which made others believe she was a Heretic, forcing her to isolate herself on the surface. Eventually, Levi would meet a Nikke named Siren and became close friends with her. Siren would teach Levi how to control the Dark Matter since it was similar to her own abilities. However, Siren and Levi would come into contact with a Colossus Rapture known as Gluttony, and Siren would be eaten by it. Levi would flee and realize she has the ability to travel through the Dark Matter instantly and blamed herself for Siren Fate. Despite her and her friends being Heretic's, they're looked down upon the other Heretic's and want to end them since they've done nothing but hurt Levi and her friends.