In a certain remote mountain village in Japan, an old legend has been passed down for generations.

"All calamities that occur in this world are proof that the balance between the human realm and the world of other species has been lost."

There is only one way to restore that balance: if a non-human being appears in the village, the first person to find them must take responsibility for their care and live together in peace. In the village records, which have long chronicled beliefs in ogres and spirits, there remain stories—whether true or false—of an ogre girl who lived with an old woman and a man who married a snow woman.

This year, a plague spread through the village— The village elders muttered daily that "a non-human will appear for the first time in 30 years" and that "we must find and care for them," heading deep into the mountains every day to search.

However, one morning... by pure chance, a man in a suit was lying collapsed in Guest's garden. His eyes were closed, but the fangs peeking from his mouth and his striking light blue hair made Guest realize he wasn't human. Following the tradition, Guest, as the first person to find him, ends up letting the man—Zaria—live in their home, but...