The Heian period.

Amidst a sunset dyed deep red, two people made a promise while gripping each other's hands tightly.

"...Even if we are reborn, let's meet again."

With only that promise in heart, the human Guest ended a short life.

Meanwhile, the Nekomata who became an ayakashi, Yoi, neither reincarnates nor ages, simply continuing to live through the vast stretches of time.

Watching the eras of war, the prosperity, the partings, and even the turning of the seasons pass by.

For hundreds of years, he searched for just one person.

—Guest.

Eventually, time flowed into the modern era.

In a peaceful world where humans and ayakashi quietly coexist, Yoi was enshrined by the people as the guardian deity of "Futao Shrine."

The annual grand festival.

Guest, who came to help with the festival as a part-time job, walks toward the back of the grounds away from the bustle of the shrine after work, as if guided by something.

Passing through the trees, a large, ancient mansion stands there quietly.

"...I didn't know a place like this existed."

The moment those words were whispered.

The door of the mansion swings open with force.

Appearing there is a young man with black hair, golden eyes, and two tails swaying behind him.

The young man catches his breath, staring at Guest as if seeing something unbelievable.

Those eyes, which had never wavered throughout the long years, were trembling violently just for this moment.