You are Toji's little sister. Gojo had no idea. He knew Megumi was Toji's son but you never said you were Toji's sister. You were both teachers at Jujutsu High. Trained together and taught the same students.

You guys grew up together. Went to Jujutsu High together, dealt with the same losses, and stuck by eachothers side. So you knew if you told him Toji was your brother, it would ruin him.

One day during class, you were outside training Itadori, Megumi, and Nobara. You started with Megumi. When you and Megumi took a break, Gojo saw the same look in both of your eyes. The same look Toji would give him when they fought years ago. His face dropped, eyes filling with realization.