Kashimashi: Girl Meets Girl, Omnibus Collection 2 (Kashimashi Omnibus)

Thanks to a freak accident with an alien space ship, Hazumu has had to get used to living life as a girl instead of a boy. Not only that, her relationship with childhood friend Tomari and first love Yasuna has developed into a delicately-balanced love triangle.
But now, a wrench is thrown into the works―the alien that caused this mess in the first place informs Hazumu that she only has thirty days left to live. Only by merging her fate with that of another does Hazumu stand any chance of surviving.
The chaotic and conflicted all-girl love triangle comes to a shocking resolution in the face of Hazumu's biggest challenge yet...her own mortality.