I been feeling that too cause in the chapter where Jaeyi is comforting Ideum about his scar he's like yeah my bro was sick too so he got lots of opportunities and even takes other people's things is his bro gonna try to take Ideum
i thought this too at first, but if i remember correctly, wasnt jaeyi’s older brother older than ideum? so that theory wouldnt make sense since the guy in the flashback was in the same grade as ideum.
I have this feeling that seme older brother is the one who showed up in uke flashback the one where they were high school OR I DON'T KNOW