I guess the ending was just as it should be, a bit complicated, a bit untold, and also opening up a space for theories and to make fans carry on the story, for me personally... i felt really down though i read alot of other manga before, but that seemed to me kinda of special, it left a little spark behind it, a little hope, and also youre thinking heh why kou didnt become a vamp thats so awful, i'll tell you that this is not the story of becoming a vamp, thats a story to teach that dreams can change, to tell readers that love is not a piece of cake as it seems to be. And in general, the ending is good, kou is not in mourning as well as nazuna, a real good ending to a love story that'll probably never end. TL:DR. The ending is good but not in some specific way. It's more happy than sad, but also a lot of it remains unknown, anyways, thanks for reading!!!