Kannazuki no Miko

On the moon, there is an old shrine that has fallen into ruin. On the birthday of Himeko Kurusugawa and Chikane Himemiya, there is a sudden eclipse, and a voice calls the eight necks of Orochi to rise and destroy the Solar Priestess and the Lunar Priestess. The two girls soon find themselves under attack by the Orochi, but Himeko's close friend Souma has resisted the call of the Orochi and has sworn to protect her, no matter what.