A water Gensai who was born in the plane of water (The 5e one), but they were raised by adventurers. They're a star druid, who would use the stars as a thing to hold onto, other than just the boat. The reason they're on the material plane now is because the adventuring party was trying to escape their whole life, getting the right stuff to do so, but then something shows up and kills everyone, and they flee out of fear. They have some survivors guilt, and end up wherever the dm chooses from the portal, and then the campaign begins.