Lizzie Doss is a primary character from Crimson Gray. She's the yandere for John.
Background
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. When John talks to her one day, apologizing for a couple of guys talking about how creepy she is.
Yandere Traits
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 in one route. 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.