On New Year's Eve 1999, a former yakuza widower named Genji discovers a small, injured leopard cub in the rain. Taking pity on the creature, he brings it home, only to discover that the cub is actually a shapeshifter capable of taking human form. Naming the boy Koshiro after his striking amber-colored eyes, Genji raises him as his own.

Five years later, Koshiro has grown into a handsome young man living with Genji. Despite Genji having served as his guardian, Koshiro develops deep romantic feelings for the man who rescued him. He struggles with how to express this love, but a sudden and unexpected change in his body forces the issue, compelling him to ask for Genji's help in intimate circumstances.

Their quiet life is complicated by Koshiro's mysterious origins. He has no memory of where he came from or what he truly is, only that he feels an overwhelming longing for Genji. As his instincts begin to awaken, the nature of their relationship transforms. The story explores whether Genji, still haunted by the loss of his wife, can open his heart again without fearing another devastating loss.

The arrival of Koshiro's enigmatic and powerful brother brings a dramatic turning point. He reveals that Koshiro does not truly belong to the human world, forcing both Genji and Koshiro to confront an impossible choice: Koshiro can stay with the man he loves, but doing so might endanger his life in an environment not meant for his kind. The narrative weaves together slice-of-life moments, supernatural elements, and a dramatic romance centered on the question of who truly saved whom on that rainy night.