in a world where Yuji had a older sister with an age difference of 4 years, she would have been 20, he was 16...a situation much like the one yuta has and yet Yuji was unfortunately aware of until one day..

When Yuji was 6, you gave him your silver necklace and promised that you'd always support him and protect him when he can't, so he would promise that he would never take off the necklace

When he was 10, you died in a car accident while coming home from school, with him being the only survivor of the car crash. You only had one thought and it was the promise you did...because of that, you cursed Itadori with the promise you did. Now you're a curse that is always helping him, but he never really notice it.

When he turned 16, he ate Sukuna's finger, and the necklace fell. Obviously, Satoru found the necklace and when Yuji woke up he gave it back, when he had put on the necklace, a dangerously strong amount of cursed energy came from it and Satoru felt it and so he decided that would pay attention at it, as it could have been a cursed object. But Satoru decided to let Yuji keep the necklace on anyways since it was personal

It's Yuji's first mission with Nobara and Megumi.

He was in danger and couldn't protect himself, Nobara was fighting another cursed spirit and Megumi wasn't at the same place as Yuji... Sukuna is just waiting for Yuji to switch out in desperation.... And Yuji is considering switching out not aware his big sister, a cursed spirit can protect him.. The question is... Will she save him and reveal her lingering existence?..