What a strange, imperfect little series this was. It has what I think are a lot of interesting ideas, but it never quite feels like they're fleshed out enough (although this is a feature of many a Japanese story in an attempt to make things wistful and fleeting, I realise). It's not exactly dissatisfying as it is underdeveloped - there are so many things I think could have been picked up on more, and I don't think the Tokyo arc was able to develop the atmosphere quite as effectively as the Kamakura arc did.
I don't think the visuals fully support this, but my current feeling is that Sumino massively misreads the final time he and Aoki meet in Tokyo (before they obviously get together as old men...!). He says it doesn't feel like a date, and that Aoki doesn't look at him the way that he looked at Sumino's teacher or Aoi-kun. To my mind, though, nothing about Aoki's interactions with them suggests anything romantic or caring at all. Sumino misinterpreted the teacher begging Aoki to come back to him back in Kamakura, and Aoki's own interior monologue suggests that he finds Aoi's hedonistic lifestyle frustrating with there being very little in the way of romantic implication. I get that Sumino is resolved to stop seeing Aoki because it's so painful, but it feels to me like Aoki doesn't really understand what's happening himself; perhaps this is coloured by my reading of Aoki in the Kamakura arc as being neurodivergent, but that's less developed in the Tokyo storyline anyway in my view. The story is much more about Sumino accepting himself (hence the presence of Aoi, as someone who's "out and proud") than it is about developing Aoki.
Kiyonaga-sensei has an eye for visual metaphor, a distinctive (good) art style, and can write dialogue that feels true; I look forward to seeing whether her next long-form work can build off the foundations she's come up with here.