Responses
I actually think the author is planning to make Hinase both genders.
I mean, the manga is called "the gender of Mona Lisa" and starts out with a teacher explaining about Mona Lisa and that paintings representation of both genders. And at the doctors office we are shown a snippet of an email about a "Mona Lisa case" which hints that it's possible to evolve into a hermaphrodite. So I think Hinase might become both.
Well I wouldn't mind if that were the end results, it sounds very interesting (๑•ㅂ•)و✧
Like many others have said in the comments, it seems like the author is kind of edging Hinase to be female. While the concept of the story is unique, as a connoisseur of gender bender, I've read 5 other mangas where the mc was genderless in some way. I'm not going to name them because then I would be spoiling the fact that all of the main characters choose to be female by the end. (⊙…⊙ )
So I hope Hinase becomes male b/c 1.it finally happened ε=ε=(ノ≧∇≦)ノ2.Ritsu > Shiori. 3.Are girls incapable of seducing the main character?! I'm looking at you Kureha Fujishima!