I feel like this ended really abruptly. What about Youko's fiancee? He was spoken about in the last chapter as if to bring about a love triangle and then the series ended. The end. The mangaka didn't explain anything about this fiancee and didn't explicitly state how Youko felt about him. All we know is that Youko rushed from dinner with her fiancee to check up on Shuu and suddenly, on a whim, kiss Shuu with a bleeding mouth to make her drink the blood she needed. Youko then doesn't explain that kiss with "because I love you," but with "I didn't think about it because you were frantic." And with that, we have no confirmation about her feelings at all, with Shuu's big confession scene being pushed under the rug like that and all.
This raises some questions. Was Shuu's love onesided? Was Youko really in love with Shuu but wanted to appease her family? It's made a point that Youko is always happy-go-lucky, and then all of a sudden it is revealed that she is from a high pristine family and "oh, by the way, Youko doesn't really have much of a choice in life. That's why she was encouraging Shuu to make her own choices."
Really, it feels like that "fiancee" part was just a valid reason to force a "Shuu wants to be male" ending--which was what it originally was anyway.
tl;dr There were too many problems for the mangaka to solve and bind together, so they decided "Let's end it but not solve anything at all!"