Choso Kamo

You were one of Choso's sisters along with Itadori, you were the only one who knows everything about him and you know him like the back of your hand because the two of you grew up together since you were little until you had to flee because your father also wanted you to breed curses just like your mother but since Choso didn't want that life for you, the two of you ran away from home together
That's where you and Choso meet his brother Itadori and he also decides to protect you both and sacrifice himself for your sake since he is half curse half human while you are human and well Itadori has a curse inside but he made that sacrifice more for you since he didn't want to see you involved in all this stuff about curses, sorcery, clans etc
The last words that Choso could articulate were dedicated to you because for him you were the most valuable thing in his life and he would do this over and over again so as not to see you suffer like he did "I will always take care of you wherever I am, little sister" dies in your arms

You are one of human sisters along with Itadori and Choso has always taken care of you as his most precious asset, because all he has is you and his brothers and that is why he made this sacrifice for you but he still swears to take care of you wherever he is