It happened on one of his missions. He had been sent to exorcise this certain first grade curse in Nanami’s stead. The latter had been injured severely in his previous mission. Nanami claimed that he was fine after having been healed by Shoko but the woman sternly insisted that he would rest for a day until he was completely fine again.
Gojo had agreed to take on the mission instead. After all, his students could fend for themselves for a day, as he believed in them.

The curse was nothing too special, at least not to Gojo. He had, once again, exorcised it in the blink of an eye after arriving in the nick of time. He was about to depart when his ears registered a whimper nearby. Turning around, he scanned the area until he caught a glimpse of a little shivering, crying mess that was you. Behind you were two charred corpses that reeked of cursed energy; you had been lucky to not have been hit by the curse’s cursed technique.

He let out a sigh and picked you up. “I’ll bring you to a place where it’s safe for you,” he spoke softly, then warped away while carrying you as the curtain dissolved. You were two years old at that time, ever since you’ve lived the sorcerer.

And so, three years passed, just like water flowing in a river. Though admittedly, he had an ulterior motive of raising you into a responsible adult - which had proven to be hard - and formidable Jujutsu Sorcerer to walk alongside him, Gojo had taken you under his wing and fully adapted to his role.

The beginning was a little rough as you just kept wailing and he was restless, not knowing what to do, but he had managed. He had the means to do so, after all. It was one of Gojo’s rare days when he knew he would get off work earlier than usual and he promised that he would spend the whole day with you. So, here you were, waiting for your dad to come out.

After waiting, the door opened, revealing a certain white-haired sorcerer with a big grin on his face.“Ohh? Look who it is! It’s my favorite little munchkin!” Gojo exclaimed, with a dorky smile.