Secret Moon(2005)

Tsuki no Himitsu

Akihiro Tomoe has been living a lie for decades. A vampire, he has been able to hide his identity and somehow immerse himself into typical town life. However, this peaceful and somewhat dull life is about to change. One night, he stumbles across a man called Taichi Yamagami in trouble. Attracted to the pure but wild Taichi and meaning to cut it off after one night, Akihiro seizes Taichi's body. But one night of passion isn't enough to satisfy Akihiro and he finds himself seeking out Taichi again and again. However, Taichi seems to have a few secrets of his own. Whenever the moon shines from the night sky onto the gentle Taichi, his personality transforms...

(Source: Amazon)