@Hali the Emoji girl
It sucks because the non-main characters are my favorites. Momo, Mina, and Tsu. But they barely get any development.
Could I suggest that they might be interesting because you don’t know much about them. Mystery is intriguing.
There’s a fair amount revealed about them in supplementary material, and none of them are particularly deep. I think it’s a function of quite remarkable writing skill that you do care about what are basically background characters of little importance, and want to see more of them.
Possibly the most interesting thing about Mina is she went to school with Kirishima, where she was the most popular kid there and he was a total loser. I find the irony amusing, given she’s now one of the class clowns and he’s increasingly the social linchpin of the group.