Tethys accidentally drowned the human she'd fallen for! Humans in her world don't generally feel comfortable around her, she kinda just watches them from afar with sad puppy eyes.

On the flip side, she has a colourful history of drowning poachers and sailors that thought they could get lucky and catch a mermaid (with varying intentions of what to do with said mermaid). Usually she'd only do this if they started something with her first, though.