Mailpo serves as a supporting character in the mail delivery system, working alongside Syrup. Her distinctive appearance resembles a pale pink mailbox combined with penguin-like features, including orange feet. A blue screen on her face prominently displays a rose emblem, while pink heart designs adorn her top.

She possesses a submissive and eager-to-please personality, especially directed toward Syrup. Though dedicated to her mail-handling duties, her inherent naivety frequently leaves her vulnerable to manipulation by antagonists. This trait fuels key incidents: attempting deliveries Syrup initially refuses leads to her temporary disappearance, requiring others to find her; hiding a cake meant for a group celebration becomes the comedic premise of an entire episode.

A significant revelation about her background emerges late in the series: Mailpo is the sentient form of a red rose Syrup planted in the Cure Rose Garden. She adopted her mailbox disguise specifically to accompany Syrup on his journeys, driven by a desire to share his experiences.

During the series climax, Mailpo becomes pivotal when drawn into a mysterious black hole. Upon her return, the letters she collected throughout her service emerge, bolstering the Pretty Cure team's strength for the final confrontation.

Mailpo holds the distinction of being the franchise's only major mascot incapable of transforming into a human form. Her design also marks a departure, being based on an inanimate object rather than a living creature.