Did the seme killed his familybor it was just an accident? I didn't know this has side sto...

Seme might be passionate and mad but he’s still somewhat sane (￣∇￣")
As for his parents, it was mentioned that a dungeon opened during a party they were in and both perished. Not much was mentioned about the older kids. Heck they weren’t even shown throughout the whole thing; just that they lived independently

He made a slave of his brother and raped him 10 times!!!
He is not sane!!!
He could have killed his parents and cover it up

I already made peace with the tags and context of this story so it’s a given it might not be tolerable for some. I just wanted to reply to your comment as a fellow reader.

I mentioned that seme is somewhat sane. By that, I meant he doesn’t seem the type to kill his parents like what you theorized. However, his hyung is his whole world, to the point of madness. During their reunion, he did just shove it in MC’s hole without lube. That’s a mad man in my book (￣∇￣")

Also, he did mention what happened years after MC was stuck in the dungeon. How their parents died was mentioned during that recap.

The number of exclamation points in your reply made me think it was a violent reaction. Hopefully I was clear and direct to the point as I could and answered your initial question. Have a good day

I interpret !!! as excitment, not agression. I wasn't trying to be rude. Maybe I didn't get my point across. Let me start over.
Look, I don't care about the rape. At this point, it's a trope in yaoi. However, the brother was brutal and the uke was terrified. He was also turned into a slave. Keeping that in mind, I think he is crazier than he lets on. I was shocked that you thought he wasn't that insane.
I wouldn't put it past him to murder his own parents.
He became a hunter a little while after the MC went into the dungeon. Then, he let scientists experiment on him. Later, he joined the army. Maybe the parents were against some of this steps. Maybe they pressured to marry a girl or something.
I can see him killing his own parents; and he was powerful enought to cover it up.
I gues time will tell wich of us is right.
Thank you for answering. I'm sorry if I came across as rude.