Someone shared the link RAW already, only few comments below mine but sadly it's only until chapter 111, but I read the ending spoiler from this site https://omoman.com/ijimeno-jikan/izimenozikan13/
Lol, you're replying to a post on my alt account from 6 years ago. I don't really remember the story anymore, but the main reason I said it was too much was because the author revealed that the MC was a piece of shit too. He wasn't really losing his morals at all, he got what he deserved as well. It just felt excessive, and then he took revenge, which felt excessive too. At that point, it really just turned into bullying for the sake of bullying.

Welp just read the RAW, if you guys expected some satisfying revenge story then you're probably gonna get disappointed, this manga is literally about "Bullying Time" a circle of bullying, MC did his revenge too far to the point it's just another bullying. I personally didn't find it satisfying. In fact this manga is literally the ultimate revenge manga, everyone just ruined other's life. Short spoiler summary, the bullied kid (not the MC) used to bully the white haired bully and the black haired bully in elementary school (Yup, They got their revenge in mid school, they successfully bullied that guy, but MC and his friend interfered) MC got dragged to this mess, one of the bully killed his cat, tried to suicide, but failed cause his mom called, after that MC got character development "The only ones who should die are the bullies" thus he paid them back cruelly, and equally (he beat the short haired girl bully really bad), then author gives us the white haired bully's flashback, and his pitiful childhood, he apologized and realized that what he did to MC was so bad, but MC still tortures him to the point you legitimately feel sorry to the white haired bully.
TL;DR everyone except MC's mother is so fucked up