The ending??? My theory is that the reason they're not allowed to breed is because the moment they do the power gets passed down and it becomes a never ending cycle, and so far nobody has been able to break that cycle as every himeko chose love over the burdening duty. If it's a women and she gives birth that's passed down to the child, and if it's a man it's passed down to the next child with the red eyes. Which I think are the only people who are capable of having this ability. Theory aside this story was great, I loved the characters and especially Yamato and his persistent and consistent his love for Shiki was, it's truly beautiful!
Hime Muko