I don't know how you could construe this as anything other than a harem, there are, right now, at least four girls in some kind of romantic situation with the main character. The core definition of a harem is that there's a singular protagonist surrounded by multiple prospective romantic interests.I say the same thing as always.
Multiple love interests doesn't equal harem.
(...)
Unfortunately people add the harem tag simply because there are multiple girls, but I don't think it works like that.
+ I'd like to add that I understand where people get the harem tag from and why people don't like reading stories with multiple love interests, unfortunately my take isn't the majority. I was just trying to explain why I don't agree with it.
Realistically speaking the dude did nothing wrong. His ex-gf disappeared from his life randomly, then 5 years passed and now he is interested in the older girl, while also having a childhood friend who likes him, but he is not responsible for that. People don't have to just accept someone's love "just because".
I mean, alright? Wasn't claiming he did anything wrong.
As for calling Mia "overpowering" is valid, but that doesn't automatically mean the other girls are filler. It depends on whether the story actually uses them to explore different emotional angles or nah.
We are still only 20 chapters in the story, and right now it's Mia's arc, which was said a few chapters ago, so anything can happen later.
I don't think it's much in the way of a prophecy to suggest the comic called "Mia has returned" will center on Mia as the story, and the other romance interests will not really contribute to the story of, well, Mia returning mysteriously, in a significant way.
I do think a narrative like this needs at least one alternate romance interest, to create the dilemma where the protagonist is tempted by something new or something that he used to know; that'd make a more tight, compact narrative. But a more tight and compact narrative is likely not the goal here - it'll probably go on for many, many more chapters before it's done, and multiple romance interests are here to make sure of that. That I think is a fatal flaw of the harem genre - after the principal cast of characters all discover they have feelings for the protagonists, pretty much any chapter other than the last becomes a filler meant to just keep the story going for its own sake. Now, seeing that there's still a lot of mystery going on with Mia, this hasn't hit that point yet.