Bloody Cross Series by Shiwo Komeyama

Half angel, half demon, Tsukimiya must drink pure demon blood to stave off the curse that will eventually claim her life. When she meets an angel named Hinata, he's eager to team up with the half-blood to take down a vampire that has been attacking humans. Tsukimiya is surprised to find that Hinata is a capable partner, but when the vampire is slain, it is Hinata who claims its demon blood, leaving Tsukimiya to be taken by the curse... moreHalf angel, half demon, Tsukimiya must drink pure demon blood to stave off the curse that will eventually claim her life. When she meets an angel named Hinata, he's eager to team up with the half-blood to take down a vampire that has been attacking humans. Tsukimiya is surprised to find that Hinata is a capable partner, but when the vampire is slain, it is Hinata who claims its demon blood, leaving Tsukimiya to be taken by the curse. In a last-ditch effort to save herself, Tsukimiya tries to drink Hinata's blood, now mixed with the vampire's pure demon blood. But in taking the blood that will save her, Tsukimiya has also transmitted the curse that will kill her. Hinata and Tsukimiya now share the curse...and they're running out of time. less

Tsukimiya and Hinata thought they had secured at last the divine power of God that will allow them to break their deadly curse, but they and Tsuzuki are not the only ones after the power. Even as Tsuzuki collects the power that will fuel his ascent to omnipotence, there is one who would see him brought crashing back to Earth. As both sides race toward the prize, Tsuzuki calls on the half-bloods Tsukimiya and Hinata to join the hunt and prevent the power from falling into dark hands...

Recovering the first Prophecy Book nearly cost Tsukimiya her life, so securing the second will be no small feat. Now that Satsuki has mobilized in the race to collect God's inheritance, he and Tsuzuki clash violently when the second Book and its key appear simultaneously in two separate locations. Tsuzuki has the conviction, but does he have the strength to defeat the fallen angel, whose determination is such that he is willing to fly in the face of God himself?

Tsukimiya has fallen into the hands of Arcana and Satsuki, but her enemies seem more interested in the mark she bears than in the half-blood herself. But what about Hinata? The intentions of Tsukimiya's former, albeit temporary, ally seem to oscillate between sympathetic and self-serving as the would-be gods plot to use her as a living sacrifice! Betrayed, bloodied, and left for dead, Tsukimiya resolves to seek the truth of the curse on her own terms--and by any means necessary...