who is he?
obvious spoilers but
He's Yuder's hyung
biological?
Nope. It's a cute thought, but they can't be because of something that will be revealed in the future.
To Yuder he's the only person who didn't betray him in his past life.
The rest is just character backstory which will be revealed eventually. Not too important at this point
ENON ! Finaly ! ヾ(☆▽☆)