Chapter 1: I am?

Here I am floating through the infinite void of darkness that is my mind, I see nothing feel nothing, and am nothing. I had given my life to save my sister's life it was a painful death, yes but it was well worth that pain knowing that my sister would live an entire life. meet someone and spend the rest of her life with him have children and die of old age. I accepted my death long ago you see my sister had been born with a disease that would slowly deteriorate over time until it was too small so I had willingly given up my heart knowing full well that she would hate me for choosing her over myself but a brother must always look after the younger sister and so here I am. in the infinite nothingness that I presume is death.

So here I lay for what I assume is forever and it seems that way unti-. "oni-chan!! wake upp!!!" I open my eyes and in front of me is a cute teen with short cute pink hair

wait I can see am I not dead I quickly tried to get up completely forgetting about the person above me and because of that I hit my forehead against hers." ahh!" she recoiled away from me I shot up off the bed and ran towards the bathroom I quickly open the door and head towards the mirror wait how did I know where the bathroom was uh nevermind I checked the mirror "ahh what the fuuck" in the mirror appeared someone I had never seen in my life he had straight black hair and bright blue eyes ( he looks like yato from noragami )

a sudden pain rushes through my head. Who's memories are these a life that I had never lived had flashed through my eyes and then finally came the memories of this bodies little sister itadori Yuji. back when I was with my little sister in the hospital we often watched anime not that I was ever that into it but I forced myself to learn everything I can about every anime we watched because they brought my sister so much happier and provided her an escape from reality so I learnt everything about each anime we watched and bought and read the manga to her while I was there and among all these anime one stood out to me the most and that one was Jujutsu kaisen. my sister loved the anime and manga so much and to my surprise so did I and that anime is what brings me to my current confusion. I looked back in the mirror and looked at the person appearing in the doorway "am I in jujutsu kaisen".