Masatsugu Nakamura, an 11-year-old fifth-grade student, is the only son of Masamichi Nakamura. Masamichi, a former drummer in Shinnosuke Kanamuro's high school band, now works at the municipal office organizing a local music festival to boost tourism.

Masatsugu develops a crush on Aoi Aioi, a high school student and aspiring bassist. He accompanies her to investigate Shinno, the mysterious 18-year-old version of Shinnosuke who manifests as an ikiryō due to unresolved emotions. Applying a scientific approach, Masatsugu hypothesizes that Shinno's physical form is location-specific and originates from the adult Shinnosuke's lingering regrets.

He actively supports Aoi's efforts to reconcile her sister Akane with the adult Shinnosuke, believing this might allow Shinno to reintegrate. Demonstrating concern for others' safety, Masatsugu participates in the search for Akane when she becomes trapped during a landslide. His involvement in the music festival preparations aligns with his father's community work, though his personal motivations include spending time with Aoi.

Masatsugu's actions reflect a blend of childhood curiosity and emotional maturity as he navigates his feelings for Aoi while pragmatically assisting with the supernatural phenomena and logistical challenges surrounding the festival and interpersonal conflicts.