Psychopath Girlfriend

Yuma is the victim of bullying by a gang of thugs at his school. His daily life is an ordeal, and he feels like he's gradually sinking into madness. The only way he can relieve his stress and keep his head above water is to wreck the cars of complete strangers. But one day, a girl catches him in the act. The girl immediately realizes that he was going through the same troubles as her. She accosts him with an offer, "Yuma, you're the partner I've been looking for for years...". From then on, they agree to support each other. Except that he didn't know that the young lady has long since descended into madness...

(Source: Omaké Books, translated)