Maybe Cain visited Korea when he was a kid, he was very lonely idk then he met jooin who willingly make friends with him. Maybe after jooin became friends with cain, Cain decided to call jooin master because he was his first friend. Then Cain left Korea but promised to comeback again. (I don't know why he said they knew eachother from past life but oh well lol) Cain comes back to Korea and accidentally meets jooin again after years, but jooin didnt remember him. That's just my theory so it's not true lol. Pls don't be mean I'm sensitive HAHAHAHAHA
Maybe Cain visited Korea when he was a kid, he was very lonely idk then he met jooin who willingly make friends with him. Maybe after jooin became friends with cain, Cain decided to call jooin master because he was his first friend. Then Cain left Korea but promised to comeback again. (I don't know why he said they knew eachother from past life but oh well lol) Cain comes back to Korea and accidentally meets jooin again after years, but jooin didnt remember him. That's just my theory so it's not true lol. Pls don't be mean I'm sensitive HAHAHAHAHA