Riku Nanase anchors the idol group IDOLiSH7, his exceptional singing voice a cornerstone of their identity. He radiates energetic optimism, often voicing thoughts directly and unfiltered, which can inadvertently lead to insensitive remarks due to his naivety about social complexities, not malice. Driven by strong determination, he pursues idol success despite significant health challenges: a lifelong, unspecified respiratory illness causing breathing difficulties and limited endurance. Frequent hospitalizations mark his past. This condition necessitates constant inhaler use and avoidance of strenuous activity, though Riku sometimes downplays symptoms to avoid worrying others—a habit that has triggered serious health scares. Childhood restrictions, like being denied chocolate for potential health triggers, caused him distress.

Riku's core motivation for becoming an idol is to understand his twin brother, Tenn Kujo, who left years ago to join rival group TRIGGER. While conflicted about Tenn's departure, Riku maintains deep care for him; their relationship holds underlying mutual concern beneath surface tensions. Within IDOLiSH7, he shares an especially close bond with Iori Izumi, who first deduced Riku's health condition and often acts protectively. The group collectively supports and accommodates his needs. Personal quirks include sitting while hugging his knees, possessing extremely low alcohol tolerance (even reacting to non-alcoholic chanmery), and repeatedly rewatching TRIGGER performances while pausing specifically during Tenn's solos. Otoharu Takanashi scouted him after hearing him sing at a karaoke session with friends.

The concert film *LIVE 4bit BEYOND THE PERiOD* features Riku performing with IDOLiSH7 and other groups but does not introduce new character development or backstory specific to him.