Kaya Mizuki, born Maya Iida, is a fictional voice actress and idol who adopts her stage name from the kanji for "water" and "tree." Her younger sister, Kanako Iida, voices the character Rarako, a role cherished by Kaya’s fervent fan Kouhei Imamura. A graduate of Seikai Women’s University, Kaya rose to prominence through her breakout role in the anime *Melting! Magical Girl Lala-ko*, establishing herself as a multifaceted talent with vocal prowess and magnetic stage performances. Her concerts consistently sell out, captivating even those like Kouhei, who rarely engage with real-world celebrities. He attends her shows religiously, brandishing glow sticks and passionately singing her songs in solitary karaoke.

Kaya shares a close friendship with Azusa Hamaoka, a senior in the university diving club, and occasionally visits the bar "Grand Blue" without participating in club affairs. While her bond with Kanako is acknowledged, the nature of their relationship is not elaborated. A narrative timeskip reveals her marriage, paralleling the real-life inspiration behind her character, though her spouse’s identity remains unmentioned.

Her arc explores the intersection of fictional idol culture and real-world fandom, exerting subtle influence through Kouhei’s obsessive devotion and her symbolic role linking comedic storytelling to themes of celebrity adoration. Though rarely appearing physically, she features briefly in a special rendition of the ending theme "Azure Al Fine," depicted alongside Kouhei’s solitary karaoke tribute. Her background, career trajectory, and thematic relevance remain consistent across official media, with no expanded appearances in spin-offs or ancillary content.