Ryōichi Kyōgoku arrives in present-day Kamakura from a future where humanity survives on the moon after Earth's environmental collapse. Posing as a junior high transfer student, his mission, commanded by his father, is to locate and awaken latent psychic abilities among the students, recruiting them to aid the future's survival. He carries a crystalline hourglass that measures time and transforms into a talking fox-like companion, later revealed to house his father's spirit. This artifact strictly limits his time in the past.

Using charisma and telepathic powers, Ryōichi manipulates social dynamics to isolate potential psychics, enforcing rules like a mobile phone ban. Despite his pragmatic goals, he forms a deep emotional connection to Earth's beauty and its people. He develops a genuine romantic bond with Kahori Harukawa after she observes him play "Claire de Lune," and comes to regard tactical target Kenji Seki as both rival and friend. His half-Earth heritage—his mother was from the present but died after his birth—fuels his internal conflict between loyalty to the future and his newfound attachments.

This conflict peaks when Kenji confronts him to stop the psychic awakening plan. During their clash, Ryōichi accesses Kenji's memories, uncovering a timeline where Kenji survived childhood only through Natsuki Suzuura's time-travel intervention and sacrifice of her powers. Faced with the choice to kill the younger Kenji and Natsuki to claim Kenji's sealed abilities, Ryōichi defies his father's spirit and spares them.

Mission failed and time expired, Ryōichi prepares to return alone to the future, knowing his existence will be erased from the present's memory. Kenji intervenes, volunteering to accompany him and directly repair the future using his unlocked psychic abilities. Ryōichi vanishes with Kenji, accepting this partnership. In a final act, his spirit briefly reappears beside Kenji after Kenji returns to the present, signifying their enduring connection.