MoonPhase is about a young female vampire, Hazuki, who is being held in a castle in Germany by her father and by his servant Vigo. One day, Kohei, who has an amazing ability to photograph supernatural phenomena despite the fact that he can’t sense them at all himself, spots Hazuki and her alter-ego Luna as he is taking pictures of the castle. Kohei goes back to the castle along with Seiji, who knows how to use ancient magic, to take more pictures when Hazuki. However, when Kohei finally meets Hazuki, she bites him, under the belief that biting him will put him under her control and help her escape the castle. However, supernatural things having absolutely no affect on Kohei, the bite has no such result. In the end, Kohei helps Hazuki escape the castle anyway, and she ends up coming to Japan to live with Kohei and his grandfather Ryuhei.
From there, Hazuki gets help from Kohei to try to find out what happened to her mother, while at the same time forces of Hazuki’s father marshal up in order to try to return Hazuki to the castle. The reason for this being that Hazuki has a secret: she is a true day walker - a vampire who can walk in daylight. If other vampires found out about this ability, they would rush to Hazuki to take that power for themselves. However, minions attempting to recapture Hazuki find another important reason to succeed: Kohei himself is revealed to be the mythical vampire lover - a human whom, if a vampire bites them, will free that vampire from any blood bonds which they may be constrained by (such as by being bitten and turned into a vampire by another vampire).
