His name is basically a pun on "just a guy"—fitting, since he's intentionally written as completely normal and average. In the original one-shot, he went by Shigeo Tadano instead.
What sets him apart, ironically, is his ability to read people. He claims his specialty is understanding the room, and he backs it up—he's the first person to actually figure out that Komi isn't rude or arrogant like everyone assumes. Where others see a cold, aloof girl, he notices something different about her right away.
He becomes her first real friend, which kind of makes sense given how perceptive he is. For someone so determinedly ordinary, that's his actual superpower.
Content compiled by AnimeList.moe from publicly available sources.
