Kappy is the title character and protagonist of the anime series. He is the young prince of a place called Kapimeshia. His real identity is that of a prince, but he is discovered by a nine-year-old girl named Suguri Kinoshita in the form of an unusual rock that she initially intends to use for a bracelet. When picked up, the rock reveals itself to be the creature Kappy, who then comes to live with Suguri and her family. By species, he is depicted as a capybara, and he serves as a magical animal companion or sidekick.

In terms of personality, Kappy has a laid-back and easygoing nature. He has a strong fondness for sweet foods, with donuts being a particular favorite. While generally cute and well-intentioned, his relaxed and sometimes careless attitude can lead him to cause trouble or unintentional problems for the people around him. Despite these minor mishaps, his character is defined by a cheerful and playful demeanor that is typical of a young child, fitting his age of three years old.

Kappy's primary motivation is his day-to-day life and interactions with his human companion, Suguri. He uses his magical powers to help resolve the ordinary problems that arise in their daily activities, such as retrieving a lost balloon, completing chores, or mending small arguments between friends. At other times, his actions might inadvertently create a new predicament that also needs to be solved. His role in the story is that of a magical friend and helper who brings an element of fantasy to the otherwise normal, slice-of-life setting.

The most significant relationship in Kappy's life is with Suguri Kinoshita, the girl who found him and with whom he lives. She acts as his partner and primary caretaker. Kappy also has connections to other characters from his home kingdom. He is betrothed to or is the love interest of a girl named Whippy, a fellow resident of Kapimeshia. He has a younger sister named Kobara, who is described as a bit of a troublemaker, and his parents, Kappy no Okaasan and Kappy no Otousan, also exist within the series' world. Furthermore, he has a rival named Dokuroppy, who views Kappy with a competitive eye.

Throughout the series, Kappy does not undergo a significant personal transformation or dramatic development. His personality and core traits remain largely consistent from the beginning to the end of the show, functioning as a stable, cute, and magical presence in the episodic narratives. The series focuses on the small, heartwarming adventures he shares with his friends rather than on a deep character arc for Kappy himself.

Kappy possesses unspecified magical abilities that he uses to solve the various small-scale conflicts that occur in each episode. These powers are the primary means by which he helps Suguri and their friends, allowing him to overcome challenges that ordinary children could not. Whether he is fixing a problem or occasionally causing one, his magic is the central fantastical element that drives the plot of each short, five-minute episode.