One day close to Tanabata, the members of Procellarum are at one of Japan's scariest haunted houses at an amusement park for filming for a television program.

On the day of filming, Fuduki Kai, one of the members of Procellarum, had a certain dream.

It was a dream that was filled with memories of Tanabata――. As soon as filming began, Kai, who was paired up with Rui, saw something

and disappeared, chasing after that something.

For the shooting of a promotional video, Gravi and Procella are at a resort island! From enjoying marine sports to a beach volleyball showdown, both groups are having their fill of the island and summer!

With the shooting going as planned, all that's left now is free time... when a tragic crime has occurred!

Without so much as a single lead on who committed the crime, Koi, claiming the title "the Great Detective Koikku", has set out to solve this crime!

Will Koikku discover the one and only truth!?