Idk, I feel like this was unnecessary. Like we've already seen the heinous abuse Cheol's f...

I respectfully disagree that it's unnecessary, or that the author is insecure. Cheol's little brother is exactly the type whose hateful behavior would escalate into attempted murder. He's emotional and irrational and hot-headed. What he just did now adds to the chain reaction of justification that Minyoung probably uses to do whatever he ends up doing (we don't know yet.) Abuse and such isn't enough to justify killing Cheol's family, but attempted murder would be. Already readers are siding with Minyoung, so it's working. All we know is that something leads to Cheol and Minyoung being separated for many years and Cheol living in terror of him. So that's likely what we're seeing here: the reason Minyoung ends up doing X.

Exactly. Cheol's near death experience was probably minyoung's last straw

Eh, the little brother is already threatening Cheol with telling everyone he's gay, laughing at him for being abused, belittling him and just generally holding great contempt towards him. If it were Cheol's father who attempted to kill Cheol, as he has previously no doubt, I wouldn't complain since he is an adult. But the fact that a teenager is doing all this ridiculously evil stuff just doesn't seem in good taste. I get that its to show how he's affected by the upbringing but we've already seen that. Also I feel like the horrific abuse of Cheol & the sense of hopelessness minyoung feels already justifies why he's willing to kill them all. Cheol being pushed to death after all of this seems over the top.

nah you’re exactly right. the author’s going for shock value but it’s just too messy and cheap imo