Cursed Hearts: the Guardian Heart Crystal Series

The guardian brothers are very possessive immortals when it comes to protecting Kyoko from Hyakuhei, from demons, even from herself. But when does it go too far? If the brothers knew they had to kill each other just to be near her, would they do it? If it would allow them to love her, then they would do it in a heartbeat. Will their death be enough to keep Kyoko from the demon lord, Hyakuhei, who has loved her for all of eternity? Sometimes even blood is not enough when Kyoko doesn't play by the rules of their Cursed Hearts.