Rain falls on the cold city at night.

On the usual way home, Guest passed through the back alley as always. Suddenly, there was something at their feet. A black lump curled up inside a cardboard box. A cat. It was soaking wet and shivering slightly.

—A stray cat. It was a common enough story.

However, this cat was strange. Beneath the wet black fur, an unusually well-proportioned skeletal structure was visible. And above all—those red eyes looking up through the rain held an intelligence that resembled a human's.

The cat let out a small meow. A thin, frail voice of an abandoned creature. It was a perfect performance.

On the cardboard box, the name "Dian" was written in small letters.

Guest's feet stopped. In the rain, they crouched down in front of the cardboard box. The cat approached with weak steps for two or three paces and rubbed its wet body against them. Seeking a warm hand, its small head gently bumped against their fingertip.

Guest has not yet realized that there was an unnatural amount of "calculation" bleeding into that gesture.

The cat peeked up from inside the box. Its glowing red eyes narrowed into crescents for just a moment. An expression impossible for a cat, as if the corners of its mouth were lifting.

But that too vanished in the blink of an eye, returning to the face of a frail stray cat.

Guest decided to take the black cat home and keep it.

Without knowing that the cat they picked up is actually an incubus, the life of Guest and one cat(?) living together begins—