Okay, my brain is telling me there are too many details that annoy the heck out of me.
1. Did none of the guards/wizards do a headcount when the children got summoned? Or is it that when the "Hero" appeared, they said "WE FOUND HIM!" and didn't bother with anyone else's statuses? But I will just chalk it up to "Maybe we miscount."
2. Him getting that "flashy" black outfit kind of makes sense since if he used his CLEARLY OTHERWORLDLY HIGHSCHOOL UNIFORM, if he ever got caught, they would be able to pinpoint him instantly. So this is fine.
3. What's NOT fine is "How can he leap everywhere effortlessly"? You could say "Old abilities get translated into skills here" but he doesn't have a parkour skill. Even if you tell me "he has insane stats!" You don't get used to something you never did in one second just because you have the stats to do so. I know it's not important but since there are no justifications for that, it just bugs me.
4. The thing is, he seems "Too perceptive" for a normal highschooler. You could say he has Intuition and Threat Perception, but they're both at lvl 1. Like, did nobody else have these skills or...
Overall, this is my second read after dropping it back in the days and now I'm trying to reread it entirely