I mean yes ofc ur point is very right but regardless dajun would have felt immense guilt period because he didn’t speak up and say what yeonju said too, “I don’t want to be split up” when it mattered the most it’s a trauma that’s deep rooted in him and his biggest regret. That’s normal to feel regret and GUILTY even if you’re a kid bc it’s like why could my brother say it but I couldn’t to him. It’s also part of why their relationship is so special and broken although yea their parents are fucking ass. Very much their fault
Yeonjun can say that cuz he can act like his age back then but dajun was forced to be matured one his parents didn't treat the twins fairly just because yeonjun is more talented than him his father favoured yeonjun I hate how his family wanted dajun to be always understanding and mature one(it's not only with yeonjun dajun has to taking of the youngest too)
I hate how they made dajun feel guilty for what happened to his twin it's not dajun's responsibility he's just a kid too they're basically the same age and dajun also grown up poorly but he couldn't blame on anyone then why his twin suddenly came up, acting like a victim and made dajun feel bad for him when it's their parents' fault