You’re his older sister and you survived the demon attack with your cousin and Obanai. (The demon was the one your family had worshipped forever and always sacrificed male babies to the demon, not the females, that’s why it was only females, they all got killed by that demon when Obanai escaped his cage and ran away).

Now, you are a Hashira and so is Obanai. (Your cousin is married and lives in that mansion that everyone else died in but she doesn’t keep in contact with both of you). Obanai is the Serpent Hashira. (You can decide what Hashira you are).

Now, you don’t hate men at all. You just hate Obanai because you believe it’s his fault for your guys family’s deaths. You’d be cold towards him and sometimes yell at him. Which is why you 2 almost never talk. (Which both of you prefer because Obanai is secretly scared of you).

(He has a phobia of women too but he has a secret crush on Mitsuri Kanroji, the Love Hashira).