I've noticed there's some misunderstanding about the popularity of this work, when viewed by a hetero-cis person.

First of all, it is not shounen-ai or yaoi manga. Those genres are written by women for women. The author, Kamatani Yuki, is not a woman and is part of the LGBT+ community. Although the main character is attracted to a guy, the story isn't about romance, but rather about understanding oneself and others. If you are looking for romance this is not the place for you. If you are looking to feel understood this is DEFINITELY the story for you.

This work was made by a queer person, with a queer perspective, for queer people. That's why some hetero-cis people may find this boring or weird. For instance, the fact that all the characters are "a label and that's all they are". I think this way of viewing things has to do that to us having (or not having) labels and coming out are very important and dear things to us, and when you are surrounded by other queer people these things come into play in the way we interact. Although these labels arent all we are, when we identify with them and we think about who we are they are always there. The characters aren't too fleshed out because we are supposed to identify with them, not fall in love with them.

One of the first things you'll hear about this manga is that it's "realistic". I can understand that in the way queer people interact with eachother (and it is not fetishized like in yaoi or yuri manga). But it is mostly realistic in the sense that almost ALL the moments in the story are present in our lives as queer people. We are hurt and we hurt people, we get worried about big and small things, we try too hard to make our friends comfortable, we get confused, we get scared, we lash out. That's why it's so popular: it RESONATES in a very specific way with us.

The only thing this story is missing is maybe more negativity. Every problem the characters have turns out well, so it might be a little bit too optimistic and idealistic. It's not like there isn't drama, but most of the drama is internal and introspective. Not much happens between characters apart from saying the wrong thing and apologizing after a while. On the other hand, its not like the characters aren't presented with discrimination, homophobia and transphobia, but it is not shown in the shape of physical violence or verbal abuse, but rather in the little things society has normilized to the point that we find them even in our safe spaces.

In that way it might give young queer readers high expectations about their future, but it might also give them the hope that problems aren't forever, making mistakes is ok and the person you are now is so different from who you are going to be.