Watching Toilet-bound Hanako-kun episode 8, and we finally get Mitsuba's official introduction in the anime.
Mitsuba is a character that is very tragic. Bullied in elementary school for acting too girly and cocky much like we see him with Kou. Thus, he figured he would change his image in middle school, and he was very plain and proper. The sad reality is that this didn't improve things because no one reached out to him. Sure, he wasn't bullied, but he made no friends, and thus it isn't too surprising Kou didn't realize who Mitsuba was. After all the Mitsuba he sees is so much different from the one he knows.
To make matters worse in come Tsukasa. Where we learn he sort of similar to Amane in that he grants wishes, but he does so for supernaturals. Though the way Tsukasa grants wishes just feels cruel and there is something different compared to when Amane did so with Nene. You can even see that he was being extra careful with Nene. Where Tsukasa manipulated Mitsuba's wish of just wanting friends to want to be remembered in such a cruel way.
The real information drop is that we learn from Tsukasa is that the one Amane killed was Tsukasa. Though given they look alike, and the only difference is the patch being dark for Tsukasa compared to white for Amane. Hard to make too much out of it at this point.
The saddest part of the episode is what Hanako says to Kou. He couldn't fix Mitsuba like he did with Nene because Nene was still living. In life, you have the opportunity to accomplish your goals and dreams. Once someone dies, it is over. It sounds like it is very taboo to do what Tsukasa is doing. Though one key thing here is that along with the flashback of Mitsuba longing for a friend we get one with Amane in the flashback we saw before. It is safe to say that Amane has regrets and likely the things Tsuchigomori mentioned before.