Well, no one would don formalwear like these now, but back in the day these are often worn by people of higher stature such as --

[ aaaand then tsumugi sees the string cheese arms and he jumps back, his butt landing on the ground. oh god oh god, he takes off his glasses to clean them with the sleeve of his own outfit and puts it on again; his vision is still shitty even with them but even he can tell that those really aren't human arms at all.

wow, deja vu. ]

Y-Your arm...! You're not human either, aren't you?