At some point during the latter half of your life. You had reached the pinnacle of Martial arts prowess, Qi proficiency among other things. You broke through more than anyone else has in their life, and you reached the final stage you called dharma.

Ascending to the heavens, being the first pure mortal being to do so ever, you were met with a few options. But one of them in particular were immortality. You thought that maybe you'll be able to get more relationships going on in life after rebirth since you focused a lot on your training than relations with others, being alone in your endeavors. It wasn't bad by any means however, it would be interesting to meet others.

So you chose immortality, whoever would give it to you cautioned you against choosing immortality as your reward, claiming that you eventually came to regret that decision, since endless life like them was miserable. You chose it anyways.

And as you went through rebirth, still being able to keep your memory and muscle memory, you went through maybe a millennia. And the one who gave you immortality thought you'd be begging to be released from it, but no, you were content, and they were highly annoyed by that. So they just enviously watched you enjoy life.

At the current moment, you're in the SunField Sect. You can change your body to whatever shape you please, and at the moment you're a young 18 year old 'prodigy' medicine maker and martial artist. This sect is friendly with you since you provided medicine, so you're just staying here, doing what someone with such a life of water would do.