King is the ruler of the magical realm known as Mary Land, a world that is sustained by the beautiful dreams of humans. Despite holding the highest office in his land, he is consistently portrayed as a somewhat incompetent and ineffective leader. His decisions are often questionable, and he lacks the commanding presence typically associated with royalty, frequently being a source of comic relief due to his bumbling nature. His wife, Queen Rumi, is much stricter and more competent, and she often scolds him for his foolish decisions and lack of judgment. He has a particular admiration for a human woman named Haruka-chan, which he secretly collects videotapes of, much to the queen's fury. When Queen Rumi discovers this, she becomes enraged, frequently threatens him with divorce, and is known to even strike him with lightning bolts when angry. The queen is also very possessive and gets jealous when she sees the king showing interest in other women.

The King's primary motivation throughout the series is the protection of Mary Land and, by extension, the human world. He has the ability to sense when the darkness threatens his kingdom, and despite his ineptitude, he understands the gravity of the situation. At the very beginning of the story, after the villains Kuromi and Baku escape from the dungeon and flee to the human world with the Melody Key, the King recognizes the danger they pose. He fears that their actions will revive the Spirit of Dark Power, which would destroy the human world and, consequently, Mary Land itself. Therefore, he takes the crucial step of appointing the gentle rabbit My Melody to be his champion. He bestows upon her the magical Melody Takt, along with other items like the Melody Box and Melody Candy, and sends her to the human world with the mission to collect Pink Notes, which generate the power of dreams needed to counteract the darkness.

The King's role is central to establishing the plot of each season. In the first season, he directly assigns My Melody her mission. In the second season, titled Kuru Kuru Shuffle, he once again sends My Melody to recapture the fugitives and prevent the Spirit of Dark Power from being resurrected a second time. In the third season, Sukkiri, the King's incompetence reaches a peak when he is put on trial by the high court of Mary Land for being unfit to rule. He is forced to resign from the throne, which sets off a new conflict where a competition is held to elect a new ruler, with My Melody and Kuromi becoming rival candidates for princess. In the fourth season, Kirara, his role shifts slightly; he visits a human girl named Kirara Hoshizuki and invites her to Mary Land, inadvertently setting the stage for that season's adventure when the Wishing Star crashes into his kingdom.

Throughout the series, the King shows minimal character development, remaining a largely static figure whose primary narrative function is to initiate My Melody's journeys and to provide humor through his flawed governance and tumultuous marriage. He is depicted as a light blue elephant who wears a red cape and a crown. While he is not a fighter, his authority as king allows him to grant magical items and mandates, which are crucial for the heroes to combat the forces of darkness. His most notable ability, apart from his royal authority, is his sensitivity to the state of dreams, allowing him to perceive when the human world's dreams are being threatened, even if his methods of dealing with the threat are often indirect and reliant on others.