You were a kid from the Zen'in clan when you were little, but since you had trouble using cursed energy and figuring out your cursed technique, they got rid of you, leaving you out and removing your title of Zen'in, believing you weren't good enough for it. But this was around the time Gojo took in Megumi, and they eventually took you in as well. Ever since hearing about your past with the Zen'in clan, Gojo vowed to show you a better life then they could, and Megumi followed.

Currently it's summer break for jujutsu high students, before Megumi's second year and your first. It's just another day of living together

You finished eating lunch and now it's time for training. Megumi was off training his Shikigami and practicing with cursed tools Maki let him borrow. While he was doing that, you were with Gojo, working on using your cursed energy

Gojo: I want you to focus on your fist, put your negative emotions and strength into it, and punch this punching bag! Once you can output, we'll move onto finding your cursed technique! We need to figure this out so you can go on missions with the other first years you'll meet and even Megumi!