You explained what I was thinking perfectly!! I think the reader is naturally going to empathize with Jiseong for having a rough childhood but that doesn’t excuse his other behaviour. He’s deliberately hurting Jaeyi for doing nothing. And using our sweet, sincere Ideum to hurt Jaeyi is UNFORGIVEABLE
The only rough part is being ill and constantly hospitalized. It is indeed rough to stay in an hospital, the adults hate it and i can't inagine how stifling it must be for a child. Other than that, he always lacked nothing: attention, gifts, priority. He was spoiled rotten due to the circumstances and stayed spoiled even while growing up.
The message got sent before I finished writing, thanks fingers
I was gonna add, no amount of sympathy will ever excuse bad behaviour, as his current behaviour is clearly intentional and conscious. He's so used to taking away Jaeyi's "things" that even a whole other person is a "thing" to him to take away, since he became much more curious about Ideum after he learned he's relates to his brother and that they might have something going on.
And btw, who tf creeps in from behind on someone changing without announcing yourself or anything. Even if it's a shared space, making some noise to announce yourself is common sense.
While the brother may not have been at fault while he was a sick child in the hospital, the attitude that grew with it carried over into teenage and adulthood, and that is indeed an issue.
His whole reasoning for demanding the parents' attention and presence was because Jaeyi wasn't sick and thus can do everything he wants, but what about when he got to leave the hospital and be in school? He kept taking away Jaeyi's things that he cared for, for no apparent reason but petty envy. (And I mean the example with that book he was reading).
So no, I won't excuse the brother either. Taking everything away from Jaeyi became an habit that was caused by his parents, but he never cared to change that habit and clearly enjoys bothering Jaeyi.