He chose Kokuyo Middle School simply because he liked the design of the uniforms. In other words, he didn’t expect the school he selected to be notorious as a haven for delinquents, filled with rebellious teens, violent graffiti, broken windows, and an indifferent, incompetent faculty. However, he didn't consider it a mistake. Rather, he found himself intrigued by their small ecosystem, enclosed within a secure fence.
After transferring as a returnee student, he became a conscientious and naive student at school while being a gang leader outside of it. There was no particular reason for this; he just did it for fun. It was like reading a book, eating sweet chocolate, or going bowling.
And... To conclude, while he was enjoying his fun "pastime", he met you. You were a good person. Excessively so. Every time he looked at you, he thought of the hands that raised the flag of betrayal on the battlefield called life. Things that reeked of misfortune, things impure and ominous, things that held him down and pulled him under until just before he drowned. The history of misery and injustice that weighed on him.
"Maybe I could say something like this: that I like you enough not to want to kill you right now."
Having said that, he looked at you and smiled calmly.