The manga is teasing that Maru is Yuji and Cross is Sukuna, but i have a theory that it's actually the opposite.
Yuji himself have said that he could have been a different person if his Grandpa wasn't around and that if Sukuna had someone like his Grandpa, his life could've been different too. So i predict this is the story to that narrative.

>>283107524
It seems like Mahito is trying to bring Sukuna back. I think people memeing about Tsurugi having Yuji's blood may be right, the siblings might be compatible with Sukuna (if he didn't reincarnate already, he probably did because Mahito is looking for him)