I try to tell myself that legitimately loving threesomes arent a thing
Er, why would you do that? They're not particularly common, but they exist.
Back to the story — the first two vignettes are very sweet and cute and fluffy, but it's the third that always brings me up short. Honoka and Kotori easily flirt with Umi, with gentle, casual intimacies. Nico catches their attention, triggering Honoka's simultaneous bragging and possessiveness — and when HonoTori leave, Nico is unsettled, but can't easily express that, or point out that the relationship between the three of them doesn't seem like "friends". The scene leaves the whole thing feeling — not quite unfinished, and not quite cut off. A little unsettling to read, I guess. Something has been left unresolved.