Fantastic manga, and a beautiful end - well, I might have been slightly disappointed, but then that poem came in to save the day ...
... anyway. I'm not saying I knew this would be the final chapter, because I didn't, but I think it was fairly obvious this was going to end soon. There were more parallels being drawn to early chapters, and characters started to look towards and talk about the future (college, career ...) more and more over looking back at their pasts, a clear indication where the manga was heading.
And I disagree that there's much in terms of loose ends. Obviously it's not like a "defeated the resurrected evil demon lord and now everybody lives happily forever" sorta end, but if we go through the characters, I don't think there's much more needed for their arcs.
Makio is Makio and was always likely to stay Makio, but she understands herself much better and learned to better recognize where she's struggling and how to deal with that, even if it's not magically "fixed" (the entire point of the manga of course being that there is nothing to "fix"). She figured out how to be with her ex-boyfriend, she figured out how to be there for Asa and how to put in a little bit of extra effort when necessary.
Ex-boyfriend is the same; he figured out much better how to be who he is and how Makio works and what her hang-ups and his own burdens are. Sure, you can say, "okay, but what happens if he finds a steady girlfriend? Or could his and Makio's romance go back to being more than sex friends? Or ..." - but that'd all be additional arcs. Their relationship at this point is very settled in what it is.
Lawyer-government-whatever dude is similar in that he's of course not magically fixed his issues but he's learned better what his strengths and weaknesses are and how to use that and mitigate any potential issues his personality might cause. We see in the last chapter how that's different from Asa's dad who clearly had similar problems with connecting to people but failed to ever get to find a way to deal with that (or didn't get the chance; maybe one day he would have).
Emily stays friends with Asa and seems fairly settled in her sexuality; I don't think there could have been more there. Obviously her occasional raging at society isn't going to be solved by some unicorns waltzing into Japan and fixing everything.
With Asa it's the same; of course it's not like all her anxieties will magically disappear but when in the beginning she was preoccupied with how to deal with her grief; trying to figure out whether her parents really loved her, where she stands with Makio, etc., she's looking forward now as you'd expect of a young person about to start college and career. Given that she's the main character her going from looking backward and overcoming that burden to be able to look forward again is about as conclusive as it can get for a (of sorts) coming-of-age story.
Even the minor characters generally were given some sort of direction for them to go to. I don't think there could have been much more than that; or if there was, I don't really know what I could have been.