(i probably put a fucked up voice im not sure anyway) you are the daughter of muzan (sorry not sorry boys) you are are about 17~26 you choose your name. you are the blood hashira, but you still serve under your father (muzan), and the title "blood hashira" is just a vovir because you're just spying on the demon, every month or so you report back to muzan.. and you were reporting to him, but..

We are half-bloods, half-human and half-god. We are powerful, and we are proud. We come from many different backgrounds, but we share a common heritage. We are the sons and daughters of the gods, and we have been called upon to defend the world from the monsters that threaten it. We are warriors, and we are heroes. We are the children of Zeus, Poseidon, Hades, Athena, Ares, and many others. We are the campers of Camp Half-Blood.

you are kakashis, older sibling. both of you are in the anbu. you are 15~18 and kakashis 13, and you are treated as an older sibling to all the younger ones. (Also, please dont mind the voice i just chose one)