Cecil Aijima hails from the desert kingdom of Agnapolis, where his people revere Muse, the goddess of music. As its prince, he embodies a cultural heritage deeply intertwined with musical spirituality, often expressing himself in poetic verses aided by muses residing in his blue necklace. His past holds political strife; relatives hostile to his half-Japanese heritage cursed him into the form of a black cat and exiled him to Japan. This curse drains his stamina when temporarily reversed by magic, requires a kiss for brief reversal, and demands reciprocated love for permanent lifting. Discovered as a cat by Haruka Nanami, who named him Kuppuru and cared for him, Cecil developed a profound emotional attachment to her.

Arriving at Saotome Academy, Cecil initially shows no interest in becoming an idol, openly prioritizing his bond with Haruka over music. His early behavior reflects royal entitlement and cultural unfamiliarity, leading to social missteps—rudely dismissing seniors like Camus and attempting to buy a shopping mall. He wrestles with Japanese customs and language, resulting in humorous incidents like failing a hiragana card game despite supreme confidence. Cecil harbors a deep fear of water and fish stemming from his desert origins, a vulnerability starkly revealed when he panics after falling into a shallow pool.

His character evolves through interactions within ST☆RISH. Witnessing their dedication and Haruka's admiration for their artistry, Cecil gradually embraces idolhood. He cultivates humility, comes to respect Camus as a mentor despite their clashes, and forms bonds with peers—notably supporting Masato Hijirikawa's acting struggles by advising him to channel feelings into performance. A competitive streak emerges during a variety show, where his spontaneous imitation of Principal Saotome reveals untapped talent and teamwork potential. His journey culminates in joining ST☆RISH, channeling royal dignity into performances while retaining childlike curiosity.

Cecil's family ties are complex. He shares a mother, Kotomi Aijima, with Otoya Ittoki—unknown to both. Kotomi survived a plane crash over Agnapolis but developed amnesia, later marrying Cecil's father. Political turmoil intensified when Cecil's uncle seized power during the king's illness, arranging a marriage between Cecil and the Queen of Silk Palace to manipulate him while ensuring his exile. Cecil demonstrates fierce protectiveness: he risks magical exhaustion shielding Haruka from threats and shows loyalty to Camus, recognizing his true nature beyond a stern exterior.

Musically, Cecil specializes in flute performance and contributes to ST☆RISH's globally inspired concerts. His theme color is green, symbolizing life and renewal. He owns a pet panther named Luu Luu, enjoys melonpan, and dislikes fish. Cecil remains ST☆RISH's sole foreign member, blending Agnapolis's mystical traditions with Japanese idol culture as he matures into his role.