ruu

I fee like that's almost every fantasy kdrama though. Son Oh Gong from Hwayugi, Alien from My love from the Star, Goblin from Goblin, etc all of them are always depicted looking like humans.

I was also a bit bother by that but I think ep 5 did an ok job explaining their past relationship. Ah Eum was the one to provoke Lee Yeon he never had interest in her. When they first met she asked if he was powerful and wanted him to serve her, it was later revealed she was a princess that wanted to kill the King. If you think about it this way Ah Eum probably befriended Lee Yeon so she could use him to kill her father (since he was the most powerful being at the mountain), but as she grew older developed feelings for him. I know their past relationship is still weird though...just trying to provide a different perspective.