Falsetto acts as a secondary antagonist within the series, first appearing as part of the villainous Trio the Minor alongside Bassdrum and Baritone. Serving under Minor Land's ruler Mephisto, the group hunts scattered musical notes to twist the Melody of Happiness into the Melody of Sorrow. His appearance features pink tousled hair, eye wrinkles revealing his age, and a signature dark red jumpsuit paired with a purple cape and white stole in early scenes. His name reflects the high-pitched vocal register, matching his character's off-key singing voice.

Before the series, Falsetto, Bassdrum, and Baritone were Major Land's protectors, the Three Musketeers. They ultimately betrayed Major Land for Mephisto. Later revelations expose Falsetto as a willing servant of the true antagonist, Noise, from the start, conspiring against Major Land's royalty even before joining Minor Land.

Falsetto's personality shifts dramatically. Initially modest and non-confrontational, he uses polite language ("boku") and defers leadership to Bassdrum despite a rotation agreement. He avoids team conflict and endures Siren's frustrations, like her clawing his hair while perched on his head. This changes drastically after Mephisto's hypnosis lifts. Noise brainwashes Falsetto, forging a ruthless, ambitious leader. His speech turns forceful, using "ore" and demanding the honorific "-sama" from Bassdrum and Baritone. Though his competence and singing improve, his actions solely serve Noise's goals, including forcibly transforming his former teammates into monstrous forms.

He actively antagonizes the Pretty Cure protagonists, frequently taunting them and mocking Cure Melody and Cure Rhythm's initial lack of synchronization. His actions escalate post-brainwashing. He confronts Ako Shirabe and her classmate Souta at their school, demanding they leave before stealing Ako's music box and summoning a Negatone monster. This attack forces Ako, as Cure Muse, to defend Souta, prompting intervention by the other Cures. Falsetto summons five Negatones in total.

His dedication culminates in completing the Melody of Sorrow. Achieving this, Noise absorbs Falsetto, deeming him expendable. Following Noise's defeat, Falsetto is released and revived. Freed from brainwashing, his original gentler personality returns. He reconciles with Bassdrum and Baritone, who remained concerned despite his harsh treatment, and receives forgiveness for his crimes, making peace with the former villains and the Pretty Cures.

Post-redemption, his appearance changes: a white ruffled shirt with a red vest, matching pants, a thin brown belt with a sword scabbard, and a short white cape featuring a jabot and red brooch.