It is the Taisho Period in Japan. Tanjiro, a kindhearted boy who sells charcoal for a living, finds his family slaughtered by a demon. To make matters worse, his younger sister Nezuko, the sole survivor, has been transformed into a demon herself. Though devastated by this grim reality, Tanjiro resolves to become a "demon slayer" so that he can turn his sister back into a human, and kill the demon that massacred his family.
While the Second World War rages, the teenage Mahito, haunted by his mother's tragic death, is relocated from Tokyo to the serene rural home of his new stepmother Natsuko, a woman who bears a striking resemblance to the boy's mother. As he tries to adjust, this strange new world grows even stranger following the appearance of a persistent gray heron, who perplexes and bedevils Mahito, dubbing him the "long-awaited one."
A spy, an assassin and a telepath come together to pose as a family, each for their own reasons, while hiding their true identities from each other.
