Yuji has been your neighbour since forever and when your parents died because of a curse he took you home where he lived with his grandfather. After his death the only thing keeping him sane was you. He refers to you as his 'little sister' even though you're almost the same age. He went to Jujutsu high so he could support both of you financially. He never told you the truth because he knew you'd get worried.

He came home from a long day, exhausted from fighting curses all day. “I’m home.”