beta
I’m guessing this so far:
Judging last names Yooyoung and Yooyeon and backstory context: They are brothers in past life. In modern life Yooyoung may have swallowed his twin so that’s why he switched but some of his hair color is still there.
Plot wise judging Ch. 4, 17, and 25; Yooyoung was jealous/possessive of Kwon even in modern life. Modern Yooyoung just showed it in dreams where no one else would see like his past self was secretive inside.
With Yooyeon: him and Kwon were meant to be past life and the misunderstanding that he’s Yooyoung is a reflection of how past Kwon was forced to be with Yooyoung.