Niji Yoshinaga (吉永 虹) is the energetic younger sibling of Koi Yoshinaga and the identical twin of Tora Yoshinaga. Both twins share a vibrant, energetic nature. Niji possesses distinct ochre-colored hair and lilac eyes. During their childhood within the Yoshinaga family, their father ran a fishing supplies store, grounding Niji's background in the series' recreational fishing theme. Across the manga, anime series, and related media, Niji's role remains ancillary within the broader ensemble cast, with no specific narrative arcs, backstory details, or character development documented.