Hi all, looking for a manga I read a few years back. From what I remember, mc is getting bullied at school by a girl who used to be friends with him. He gets offered to participate in some game where he can select anyone to be confined for about a week(not sure about this, could be a month) and if he can keep them from guess his identity, he gets money, but if he loses he goes into debt.Over the course of the game, mc slowly becomes more deranged as he tortures the bully and reveals his identity to her pretty early on.There were also other participants in the game including another guy who picked some random rich lady as his victim because he needed the money for his daughter's hospital bills and because the lady is nice.

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I'm literally a rock.

I think that's Prison Lab
https://www.mangaupdates.com/series.html?id=131481