Riku is a male Myumon, a fox-like species, with a pink nose and inner ears, teal eyes, midnight blue hair featuring a distinct ahoge, and indigo ears and tail tips. His ears match his hair color in animation. He wears a mint suit with long sleeves, matching pants, white shoes featuring brown soles, a white shirt, and a long red tie.

As bassist for the band Trichronika, he performs alongside his twin brother Kai (drummer) and admired leader Shu☆Zo (guitarist/vocalist). Their band was the first in their series to have a concert interrupted by a dark monster, requiring rescue by Cyan.

Quiet and hardworking, Riku often battles self-doubt about his musical skills. He sees himself as the weakest member of Trichronika, feeling he holds the band back. Despite his shyness, he possesses strong determination and deeply respects Shu☆Zo, aspiring to be like him. His relationship with Kai is emotionally distant and marked by poor communication; Riku is unaware of parts of Kai's life, like his work as a dance instructor, contributing to Riku's isolation. His trait scores are Determination (9), Vigor (6), Courage (2), Drowsiness (6), and Secret (9).

His interests are reading and band practice, though he struggles with dancing. His name "Riku" means "land" in Japanese, positioned between "sky" (sora) and "sea" (kairi). Official media consistently portrays his dedication to the band, admiration for Shu☆Zo, and complex relationship with his twin.