Hiroshi Tanegashima, also called Hakashi, is a 12-year-old Earth-born boy. He is the younger brother of Mina Misasa; their differing family names stem from their parents' divorce. Hiroshi journeyed to the Anshin space station with his sister under Deegle technology company's sponsored underage space experience campaign.

Unlike Mina, who dislikes space but seeks social media opportunities, Hiroshi is fascinated by space exploration. He displays extensive knowledge of space topics and conspiracy theories. Hiroshi intensely admires Touya Sagami, a child born on the moon, and knows Touya's background and significance as a "moonchild."

During the Anshin station crisis triggered by a comet collision, Hiroshi is stranded among children without adult supervision or reliable internet. His expertise in conspiracy theories aids the group as they unravel mysteries behind the station's malfunctioning systems and the threat of a technological singularity. Hiroshi's knowledge helps the group grasp the disaster's broader implications, including the role of advanced artificial intelligence like the renegade entity Seven.

Hiroshi's perspective, shaped by his space fascination and admiration for Touya, often contrasts with other characters' more cautious or pragmatic approaches. His presence underscores themes of youthful curiosity and the integration of diverse viewpoints when facing existential threats.