Made an account just to put some of my thoughts into this ending.
I watched the anime a few days ago and loved so much this universe and the main couple that, as soon as I knew the manga just had finished, I could not help but read it to know how their story ends. And I have to be honest here, I am really glad that I had the opportunity to read everything in one go, because if I'd been following the manga for 4 years, I would be even more frustrated than I am right now.
Given this, did I like this ending? No, I would like to see at least a little more affection in their reuniting. C'mon, not a single hug? A kiss? Not even a "I missed you so much" with some tears? What the author was thinking? Now, it was a good ending for the two? I mean, a good ending for Nazuna and Kou on their perpesctive? I believe it was, as things such as hugs, kisses and even sex is inevitable to happen between them from now on, we were just denied to see any glimpse of it. Denied that little shot of dopamine most of us wanted and needed.
Also, we have to remember Kou now is still just a 17-years-old teenager, he still has PLENTY to live and learn (without mentioning his half-vampire status, which makes a more than reasonable assumption that this factor at least slows his ageing at some degree). Furthermore, as a child, he pretty much bested every single other vampire he fought, and even Kiku, an elder vampire, was concerned of the idea of fighting him. Now he has even more control of his power, has combat-training, and the detective skills from Miss. Detective. He became a league of his own, probably one of the most powerful characters in this universe as far as we know.
And now that they both acknowledge their love for each other, and are willing to live together forever, they will have much time to figure out what they are, what means to be a half-vampire and a born vampire, and if it has any weight on their relationship. This ending is like a whole new beginning for them, to have new adventures, to meet new people and of course, to love each other.
But again, I really wish we had a little glimpse of this future, I think the reader deserved this, to see them as a true loving couple for once. That is why I am not satisfied with it, unless there is more to come, which we can only guess if it will ever happen. But at least I am glad and relieved it did not end in stragedy, which I was really afraid of.
PS: Screw that Hokkaido arc, too much time wasted on Seki and Kiku. It is alright to develop side stories, but invest so much time on a couple that I cared so little instead of the main one? Especially when you only have 200 chapters to explore it? Really?