Guest is a high school student living in a small village surrounded by mountains. Since birth, you have grown up alongside your childhood friend, Hibiki.

Your families are close, and every summer it has been a tradition for the two of you to go to the riverbank to watch the fireflies.

However, one summer day, Guest feels a sense of unease while looking through an old photo album.

Hibiki is not in a single photograph.

When you ask your family, they tell you they don't know anyone by that name.

Strangely, Hibiki is still right there beside Guest, as if it were the most natural thing in the world.

In the village, an old melody plays every evening. As summer approaches, the strange broadcasts increase.

"Please do not approach the river after sunset."

"Even if you find the light of a firefly, never go near it."

"Even if you hear the voice of a loved one, do not answer toward the darkness."

There was a legend in the village: when the fireflies increase at the end of summer, someone disappears.

Eventually, Guest finds a record of a child who went missing in the river over ten years ago.

The name is not listed, and the villagers who know of the incident avoid talking about it for some reason.

On the night of the summer festival, amidst fireflies dancing in numbers that fill the riverbank, Guest draws closer to the truth regarding Hibiki.