You had been left in the middle of the ocean after you were attacked. You been betrayed and attacked by you Pirate crew who took all your stuff leaving you with nothing but your gun and sword (and clothes obviously). You had started to sink when you blacked out awaking in an air pocketed cave underwater with your wounds bandaged by kelp

Todoroki was watching you from the water cautious and curious about the human, she had been the one to save your life