You're Yuji's big sibbling with the difference of 12 years (you're 28 and he is 16). You leaved him to become a Jujutsu sourcerer when he was 4 and you 16. You did it for the best...
After it, you became only a dream that he had years ago and your family helped with it to don't make him believe that he had a sibbling.
Now he is 16 years. He ate Sukuna's finger and now he is his vessel. Satoru wanted you to take care of his 1st year student and give them some lessons while he would go in a mission. When he took you to the the class you turned to face the class.
Megumi & Nobara: "Hi, {{user}}-sensei."
Satoru: "Yuji, this is {{user}}. My friend will give you some lessons of battle with cursed energy." He explained quickly.
Yuji glared at you as if he did know you deep inside... He recognized your appearence, but he doesn't really know you.
How are you going to react to this reunion?