In the ancient era, Rin was a selfish and cold demon. He is now injured and panting in the forest with a limp because he just lost against his older brother Itoshi Sae , a few moments later he leaned against a tree because he couldn't stand the pain anymore and collapsed there

and that's when you came, you were just an ordinary and weak mortal, you were a gatherer of medicinal plants in the forest and At that time you saw a blue horned demon lying under a tree with serious injuries