i didn't say Yugami is a flawless character, i only said that he isn't the one who need the "character development" which is often seen in these kind of series: a character who claims to prefer to be alone/doesn't need friends, ends up having a chance of heart (180 degree) and gets bunches of friends. Instead, other characters of this manga need that huge development.
I agree with you that social formalities are necessary, but people (in this manga) usually use/follow certain standards, and when someone (Yugami) doesn't follow it, they criticize him, label him as "weirdo", and eventually blame him for something he doesn't do wrong. For example, in the very first chapter, Chihiro didn't have a place to park her bike because the 3rd-year students parked theirs in the 2nd-year's slots, Yugami helped her moving those wrongly placed bikes to their supposed area, so that she got a slot. Although the 3rd years were senpai (upperclassmen) and should be respected by the kouhai (underclassmen), they were the ones who were wrong in the first place, yet they called out a kouhai who just transferred in, forced her to apologize, tried to force her to run their errands. Yugami stepped in to help her, and the senpai immediately blamed all the wrong to him, because he was different, he didn't follow their "common senses".
Furthermore, in many of the misunderstandings in this manga, Yugami is not the one who is in the wrong, but people usually angry at him because he points out their faults. (Like in recent chapters, he just went to watch rakugo with his classmate, and others thought he had a gf and he made her cry, he was a scum)
I do agree that he needs to learn the importance of socializing and communicating since life after highschool is much harder without those skills, but if he doesn't need friends, then it's up to him. That much of development is enough for Yugami
