In my opinion, we've seen a little bit of that. He does change only when Minyoung drives him to do so. At first Cheol was like a lone wolf, then Minyoung breaks through his barriers and he became more open and trustful. He represses what he feels but Minyoung forces him to be more honest to himself, to accept his flaws and urges. Cheol may seem passive but when his buttons are pushed, he can become aggressive (not sure this one a good point tho). But I do agree that he's so passive, but yeah he's just an high school boy that tries to fade into the background (or not, I may have to reread the story)
Honestly I get why he has truama but I dont like the love story as much if the only reason the couple is together is because one of them needs the other to survive or to live. I don’t need cheol to be like minyoung or to help or save minyoung, I still love their dynamic in which Minyoung is the protector/psycho and that’s cool

I love cheol but hes a very passive character that just reacts to stuff. Things just happen to cheol or people do things to him and he’s standing around most of the time letting it happen with red cheeks lol Kind of like a side character sometimes. I really wanna see some character development as the manhwa goes on. He and many other tops seems to only have one type of personality and that’s it. Complex characters are so much more interesting like minyoung seems like a real person. A psycho but still a real person.