I don't think so, it was Jooin that made him change by constantly rejecting him. Sure he got jealousy but his change had nothing to do with Cain. That's why some think Cain wasn't served a proper plot device. You can really remove him from the story and it won't change anything. A character is suppose to give some purpose where if you remove them they will affect the story but here it doesn't work.
It's a love triangle that's why Cain appear, you see... the conflict in Cain charater is he was trap on his past so the resolution on that is to free himself from the past which it did happen so I don't see why you'll still mad on the development of the story? The Author just not wanted Cain to be the endgame coz from the start the story really revolve bet. Jooin and Yahwi the only problem that I see on this is that maybe the author should give us a couple of chapter were we can see the reconsilation of the two so we could really appreciate the progress bet. Them.
That's what I'm thinking basically to set Cain free from his past but my problem lays with what was the purpose of it if it had nothing to really do with the main character and his story.
I get love triangles but love triangles will have both mls have a certain purpose for the mc. Story wise Cain didn't give Jooin something he will remember through his life.
So Jooin purpose was to set Cain free but what was Cain purpose to Jooin story. That what others are asking.
If author wanted to show character development of ml mc then why added third character. It makes no sense! Cain's appearance doesn't make sense if it didn't affect the end game. Like author could have shown Yahwi and Jooin took break, time skip boom they're together again like?? Yeah good for them they sorted out. But why did they even give Cain heartbreaking backstory man. Don't get me wrong I liked the guy but why show him on poster and all if his presence doesn't affect the storyline at all. He deserves better at least give guy his happy ending..