Cecil Aijima, born to the king of desert kingdom Agnapolis (Agna Palace) and Japanese mother Kotomi Aijima, faced persecution for his mixed heritage. His royal relatives cursed him into a black cat form and banished him, exploiting his father's illness to seize power. Breaking the curse required true love's reciprocation, though kissing or magic could grant temporary human transformation at the cost of his stamina.

Drawn to Haruka Nanami due to her connection to Agnapolis's goddess Muse, Cecil—as the cat Kuppuru—accepted her care before revealing his human form. He shared his background, growing fiercely devoted to her. Cecil has dark brown hair, tan skin, green eyes, and a purple tattoo on his upper right chest. He perpetually wears a blue Agnapolis necklace housing muses that craft spiritually resonant poetry, linking humans to gods.

Initially reluctant about idolhood, Cecil joined Saotome Academy solely to remain near Haruka. His royal upbringing sparked cultural misunderstandings, occasional bluntness, and flashes of entitlement. He clashed with mentor Camus, dismissing guidance until inspired by Haruka and STARISH's dedication. Committing fully to singing Haruka's compositions, he embraced humility, teamwork, and Japanese cultural nuances while retaining wide-eyed enthusiasm for new experiences.

Cecil shares a maternal half-brother, Otoya Ittoki, though neither recognized their bond. Their mother Kotomi bore Otoya with Shining Saotome before a plane crash in Agnapolis caused amnesia; she married Cecil's father and later returned to Japan, potentially due to schemes by Cecil's uncle. This uncle orchestrated an arranged marriage for Cecil to a queen, aiming to exploit his lineage while exiling him from Agnapolis.

Throughout his idol career, Cecil collaborated with units like STARISH, often partnering with Camus, Ranmaru Kurosaki, or Otoya. Specializing in flute performances of emotional depth, he channeled spiritual resonance. His desert origins bred fears of water and fish, triggering occasional panic. Despite early friction with STARISH members like Syo Kurusu, Cecil's sensitivity and observational skills enabled pivotal advice for their growth. His rivalry with Camus evolved into mutual respect, with Cecil uniquely perceiving Camus's true self.

Cecil aided Haruka against supernatural threats, gathering scattered scores to combat a Satan-possessed Shining Saotome, cementing his protective devotion. His curse permanently lifted when Haruka's love song conjured magical light, restoring his humanity and igniting their romance.

Later, he matured into a reflective, supportive idol-industry figure, balancing royal duties with artistic passion. His journey embodies adaptability, camaraderie, and the ongoing navigation of his dual heritage.