To vampires, rape is a form of love making.
Thus, their rapes and attempted rapes aren't so much evil as they are a manifestation of Blue-and-Orange Morality. Tachibana can reproduce
Hybrid or not she did get a dose of Karins magic blood, and reacted to it When Sophia was freed so was the vampires dependance
While Sophia was the key to vampire fertility she was also what stunted it. But now that she's free so are the vampires. When Usei Kanon grows up she'll become a fertility doctor
Seems like a good career for the former goddess of vampire fertility.