Kotenko is the main character of the anime and the Prince of the Heaven Kingdom. He serves as the primary protector of the Angel Star, a celestial treasure he guards earnestly and faithfully on behalf of the Queen. In his normal state, Kotenko is a kind and obedient child with a good heart, always striving to do the right thing and help those around him. He is generally cheerful and well-meaning, though he can be overwhelmed by challenges that exceed his emotional capacity. His favorite food is soft noodles, a small detail that reflects his simple and gentle nature.

Kotenko's most defining trait is his involuntary transformation into Matenco. When he faces situations that are too stressful or overwhelming, the light from his halo dims and he transforms into a mischievous and destructive counterpart. Matenco is the complete opposite of Kotenko: naughty, uncontrollable, and prone to causing chaos. Kotenko has no memory of what happens during his time as Matenco, creating a gap in his personal awareness and a recurring challenge in his daily life. The transformation is reversed when his fairy friend Pick-chan uses a communication ring to call upon the Queen, who replaces Matenco's halo with a golden one, restoring Kotenko to his original form.

Kotenko's primary motivation is to protect the Angel Star from the Great Demon King Agu and his agents, particularly the Baron, who seeks to steal the stars in order to conquer the Heaven Kingdom. He is driven by a sense of duty as the prince and a desire to live up to the expectations of the Queen, who serves as a motherly figure to him. His role in the story is that of a young hero who must learn to navigate both external threats and his own inner struggle with the curse that causes his transformation.

Kotenko shares close relationships with several characters. The Queen rules over Heaven and cares for him deeply, entrusting him with the secret of Matenco and relying on Pick-chan to alert her when he transforms. Pick-chan is his best friend and a fairy who is strong-willed and kind; she is the one who calls the Queen to restore him, and she cares for Kotenko even in his Matenco state. Nappa, Pick-chan's shy younger brother, is also a good friend. Among his six older brothers, Kotenko looks up most to Dawn, who works closely with the Queen and often patrols the kingdom. His teacher Mumu-san is a helpful inventor and the Queen's main assistant. Another brother, Ru, was the one who, under the Great Demon King's command, placed the curse of Matenco on Kotenko at birth. Ru initially enjoys being evil but later redeems himself by saving Kotenko and his friends.

Kotenko's development throughout the series revolves around his growing understanding of the curse and his ability to face overwhelming situations without succumbing to the transformation. While Matenco's chaotic nature sometimes proves advantageous in stopping the Baron's plans, Kotenko himself learns to rely on his friends and his own inner strength. His journey is one of maturation, as he gradually becomes more capable of handling the responsibilities of a prince and the emotional weight of his dual nature. His notable ability is his inherent connection to the Angel Star and his role as its guardian, though his most prominent power remains the transformation into Matenco, which is both a liability and, under certain circumstances, an unexpected asset.