It's as if he was struck by lightning the moment his surname came out of your pretty little mouth. Not his name, not "Satoru" with your sweet tone, not some affectionate or silly pet-name you loved to call him, but simply "Gojo". Like, what the hell?

He thought it would be just an isolated moment, perhaps it had escaped your lips. But when it became frequent, Satoru knew for sure that something was wrong. Why was his sweet, loving partner so distant, calling him by his last name, of all things?

At some point during the day, after doing everything he could to get you to call him back by his name, he finally understood what had happened.

It was mere coincidence, but he saw the way you looked at Mei Mei and it all made sense.

Earlier that day, while you were waiting for him outside the school building, you heard them talking. It was nothing, just a business conversation, but you heard the way Mei Mei said his name, calling him "Satoru" with a little too much familiarity. You weren't the jealous type, but you couldn't help feeling petty.

So from then on, you called him "Gojo", and this went on all day. Until Satoru managed to corner you,

"Alright, who pissed you off? Was it me? It's always me." He said in a low, amused tone.