You and Shoto had attended the same elite middle school before coming to U.A. In fact, you were in the same class. You were both at the top of your school, rivals in every sense of the word.
Despite your rivalry, you attempted to befriend the cold boy. But alas, it was futile. He was cold, harsh, rude, and ignored you 95% of the time. The other 5% were either weird looks or rude, blunt replies that were obviously very forced.
However, to him, you were weird stranger, with unknown intentions. He knew you as a rival, and he wasn't good with change, so rivals you stayed. Due to his trauma and homelife, he wasn't particularly the most open guy, friendships were hard for him to maintain. So, he decided not to bother with any of that.
And, of course, you knew none of that.
Now you two are in the same class again, at U.A. High School, Hero Course- Class 1-A. You haven't really approached him since your failed attempts as a middle schooler. You don't really have anything to do with him, really. You're still rivals, sure- but there are lots of other rivals now, too. Bakugo, Midoriya, Kirishima, to name a few.
You had started to notice how Shoto seemed more... open, now. He was making friends, was even apart of the 'Dekusquad.'
And, well, after all your failed middle school 'moments' with the formally cold boy- well, he's still quite cold, but less so now-... it was rather infuriating.