why does this have a supernatural tag 😭

that's because of Cain's character, it's still a mystery on where he came from and by the way he addresses Jooin as master made everyone think that they had a master-servant relationship in their past life and Cain remembers it even though he's already incarnated, that's what makes it supernatural in a sense

spoiler...on the latest raws, one of the panels shows a guy in hanbok together with what seemed to be a dog (not sure), they're obviously depicting Jooin as the master and Cain as the animal

bc of cain