Kikai Densen

Wearing the mask of an honor student, Seiji Tsujimi believed the world was at his command. On that day, he made Toshiyuki Aimura, a target of bullying and a plaything, the laughing stock of the class, venting his pent-up frustrations. However, Seiji had chosen the wrong path. Toshiyuki committed suicide. Toshiyuki's death left Seiji with a void in his heart, but Toshiyuki, supposed to be dead, returned as a monster. Reduced to a monster, he began to threaten Seiji's mind and daily life with humiliation and violence.
[...Forgive me...]
In this cruel and twisted world, I certainly xx you. Beyond the realm of mistakes, what do you gain, what do you lose? Feelings, curses—they spread like a contagion.

Source
https://twitter.com/KIKYU_DO/status/1774043901265150329?t=jLr1sm5fbetv4qelVJITSQ&s=19