
The only way there can be character development in this story is for Jooin to break things off with Yahwi, regardless if he turns to Cain. His relationship with Yahwi is toxic and abusive (mentally/emotionally). You could say he's been staying around hoping that Yahwi will redeem himself, but with this latest chapter I think there is no redemption now. He's had so many opportunities. Jooin deserves better and I hope he realizes it.
Where are those characters from in the ending credit picture?
From Hinekure Chaser
Thanks!