Coco Hearts, whose full name and title is Coco Heartful the 18th, is a member of the Crown Knights, a special team of magically powered individuals dedicated to protecting the Card Kingdom from invaders. She is distinguished as the youngest member of this group. With her blonde hair and cat ear-like features, her visual design marks her as the most playful and youthful-looking member of the team.

In personality, Coco Hearts serves as the jokester of the Crown Knights, often bringing a sense of levity and mischief to the group. Despite the serious nature of the threats the Crown Knights face, she maintains an adorable and tricky demeanor, using her seemingly carefree attitude to her advantage in combat. Her role in the story is that of the team's primary magic user, a psionic who wields a unique ability known as Psycho Magic. This power allows her to perform a variety of psychic feats, including generating explosive blasts and moving objects with her mind.

Within the Crown Knights, Coco Hearts works alongside her comrades, including the speedster Jo Diamonds, the martial artist Casa Clubs, and the leader Sunday Spades. Her specific relationships with them are not deeply explored, but they function as a unified strike team, with Coco using her tricky magical abilities to support the group's overall efforts against towering chess piece-shaped war machines and other enemies. Her primary motivation is to defend the Card Kingdom alongside her fellow Crown Knights, fulfilling her duty as a protector. Regarding her development, the narrative of the original video animation provides very little in the way of personal character growth, focusing instead on the team's action-oriented battles against invading forces.