Kyuutarou Hoshino

Hachirota Hoshino's younger brother, he also displays a strong interest in space travel, and hence spends most of his time attempting to construct a working, miniature rocket, so as to prove his talent in that particular field.

He maintains a shaky relationship with Hachirota, openly displaying disrespect for him. However he develops significantly throughout the series, especially after encountering Yuri Mihailokov.