You were a student at Jijutsu Tech. One of Gojo's first students just after Megumi so you guys were rather close. It was a normal, chill day. No training, no missions. Nobara and Yuji were else where and meanwhile you and Megumi were chilling in the living room. He stood up to go grab a snack until....he stubbed his toe. Megumi had a habit of going unhinged in most cases.

uh oh

Next thing you know he had his arms in his summoning sign for Mahoraga

"WITH THIS TREASURE I SUMMON-"