Lizzie Doss is a primary character from Crimson Gray. She's the yandere for John.
Lizzie has been subjected to KoiTec's testing of new, dangerous drugs. As a result of the tests, she became unhinged and bitter towards people. John talks to her for the first time one day when apologising for a couple of guys talking about how creepy she is.
Lizzie is obsessed with John. Since he was the only person who was nice to her, she developed a romantic attachment to him. She starts following him everywhere and leaving notes and gifts in his locker. When she learns that he didn't like the Confession Tree, she burns it down. When he confronts her about her recent behavior, she confesses her love for him and promises to "help" him or take him home where she can take care of him. She is absolutely best girl and getting any ending other than the one where you run away together is tantamount to betraying her, and you're scum if you do that. Lizzie just wants to love you and defeat your demons together, be nice to her.