Midsummer Equation

The summer sea, fireworks, a boy... and a mystery that must not be solved.

Manabu Yukawa, a physicist, is invited to speak on the panel of an explanatory meeting for a seabed mining plan in Harigaura, where the beautiful sea remains untouched. There, he stays at a family-owned inn called "Rokuganso".

Yukawa meets a boy named Kyohei on the train heading to Harigaura. Kyohei is the nephew of the proprietress of Rokuganso Inn. He had come to visit his aunt and uncle by himself during summer vacation because his parents were busy with work.