Riki Muroi, a bold and athletic twin grandson of Gōken Muroi, grows up alongside his reserved brother Gaku and the protagonist Persia in Africa before relocating to Japan. Known for his energetic involvement in school activities like American football, he contrasts Gaku’s quiet demeanor, often embodying an outgoing, protective older sibling figure to Persia. Unaware of her romantic feelings for him and Gaku, he remains committed to his girlfriend Sayo Mitomo, anchoring their interactions in loyalty despite growing complexities.

As Persia’s hidden magical identity emerges, Riki grapples with admiration for her alter ego while steadfastly prioritizing his relationship with Sayo. This duality sparks tension when Persia’s supernatural actions ripple through their lives, testing loyalties. Though occasional rivalry surfaces with Gaku, Riki ultimately respects Persia’s choice to pursue his brother, shifting from guardian to supportive confidant who champions her independence.

His impulsive tendencies—like recklessly seeking Persia during her disappearance—reveal a fiercely caring nature, balanced by a sociable charm that cements his popularity among peers such as classmate Yoyoko Manabe. By the series’ end, he sustains his bond with Sayo while gracefully accepting Persia’s decision to build a future with Gaku, demonstrating emotional resilience and maturity.

No additional details regarding his portrayal in spin-offs, films, or OVAs outside the main series are provided.