Cecil possesses a devoted love for Haruka, both in the games and in the anime. Haruka cares for Cecil because he was the cat that Haruka took care of, and they are usually seen together when Haruka is alone or depressed. In the second season, he tells her that her songs saved him and he confesses his love for her, much to the other boys' dismay, but since romantic relations aren't allowed, he tells her that he'll always be by her side and desires to only sing the songs she writes for him.
In Season 4 Episode 1, after STARISH pull Haruka away from QUARTET NIGHT, Cecil holds her and says that he "wants them to become one through her music."
ST☆RISHIn the game, he gets along pretty well with the other ST☆RISH members. Cecil gets along very well with Otoya, who he feels that he can be comfortable around and depend on. However, he is wary of Natsuki, because Natsuki found him cute and liked petting him, especially when he found out that he was the black cat all along. However, despite his annoyance, Cecil and Natsuki get along and Natsuki offers to teach Cecil their Japanese culture.
In the anime it is the opposite: Natsuki and Cecil got along fine from the beginning, but the other members of ST☆RISH had trouble accepting Cecil.
His assigned senior is Camus, who he often struggles to get along with. At times, he is frustrated when he cannot impress Camus or meet his standards.
Cecil admires and respects Ranmaru, the senior he was assigned to during the Shuffle Unit Project. He often flatters and is friendly with the upperclassman, despite Ranmaru's initially bitter demeanor, because he is inspired by his "bright soul" and respects his "strong voice". They are on good terms with one another, to the point of Ranmaru helping Cecil one on one during a recording in MUSIC 2's memory novel.