Under a Pale Moon

Toshun was born with a spirit's heart inside his body. This overwhelming power was too strong for his mortal frame to contain, and thus shortened his lifespan. Already steps away from death's door, he heads out into the mountains to return the heart to its rightful owner. Once there, he meets a beautiful spirit named Chofu, who tells him that centuries ago, Toshun's ancestor was the one who stole his heart. To help make amends, Toshun agrees to enter into Chofu's service. But, on the night of the full moon, a sweet scent lures him to the most enticing scene...

(Source: Animate International)

Note: Includes one extra chapter.