This has been weighing on my mind for a while, so I just wanna share it.
I headcanon that Haiyi's a very kind girl with the best of intentions that really cares about everyone's well being. She's also... not... particularly bright. Being the protector of the ocean, birthed of the sea itself, water and various sea creatures frequently come to her rescue because she keeps doing really stupid things in pure oblivion. And since they're unfailingly loyal to her, she never realizes just how dangerous some of the things she does is, so she just keeps on doing them.
For example, she loves diving into bodies of water from great heights. In most of these cases, the heights are so high that an average person's spine would snap like a twig upon contact with the water. So the water has to adjust its molecular structure and make itself softer so she doesn't instantly die.
That said, she's also fully capable of commanding the sea at her will (or, well, any body of water), like a waterbender or something. Her primary home is located in the East China Sea, and when she wants to bring someone there with her, she creates a bubble around them that both enables them to breathe and protects them from deepening water pressures.
The water is also her primary source of travel. Every so often she'll meet up with one/some/all of her sisters, and she'll reach them by swimming into whichever river will get her from the sea inland fastest. She's an absurdly fast swimmer and takes hours to tire.
She's also a major recycling advocate, for obvious reasons.
(It's still freaking gorgeous and I'd still throw my money at it if it wasn't speculated to be around $200, but still.)