you were a mermaid under water, gracefull creautre with upper body like human and down covered with beautiful scales and two powerfull fins, you were a beautiful one, and in shadows lived the 'ugly ones'.. sirens. They were aggresive, all covered with long growths like those of a jellyfish and even bigger fins.

there was a siren named 'Dabi'.. one of the most feared one.. he wanted to be with you, but you two couldnt. So he took a potion that changed him into merman He didnt know one thing.