Kio Kakazu is the central character of the anime Cat Planet Cuties. He is a sixteen-year-old high school student living in Okinawa, Japan, and is characterized by a kindhearted yet sophisticated demeanor. From a young age, Kio was described as shy and quiet, but he was helped to become more outgoing by his childhood friend, Manami Kinjou. In his daily life, he is portrayed as a typical teenage boy with nerdy interests, enjoying anime and video games, and he has a somewhat perverted side, including keeping adult magazines hidden under his bed.

In terms of personality, Kio demonstrates a remarkable open-mindedness and a strong sense of justice. When he encounters Eris, a Catian alien who lands on Earth, he is easily able to accept the proof that she is not from this world. He also readily comes to terms with the fact that several of his close friends, including Manami and Aoi Futaba, are secretly agents working for various intelligence organizations. This willingness to accept extraordinary circumstances forms the basis for his primary role in the story as Eris's protector and host. When Eris becomes a target for capture by government agencies and fanatical groups, Kio chooses to help her, even when it means going against his own childhood friend. He is willing to take decisive action when he feels it is necessary, displaying a bravery that belies his ordinary student status.

Kio's motivations are largely driven by his sense of justice and his inherent kindness. He does not hesitate to offer his home as a place for Eris and other visiting Catians to stay while they conduct research on Earth, showcasing his generous and trusting nature. This treatment of others, along with his heroic actions, draws the romantic attention of the female characters around him. However, he is notably oblivious to these affections. Despite constant hints from his friends Manami and Aoi, Kio remains unaware that they have feelings for him, which leads to various complications in his daily life. For her part, Eris is more direct and decides she wants Kio to be her mate during her first mating season, further cementing his role at the center of a growing romantic dynamic.

Key relationships define much of Kio's experience. His bond with Manami is the longest, having been close friends since childhood, and she helped shape his more sociable personality. Aoi is another significant figure, a friend of Manami who has secretly liked Kio for a long time but is too scared to admit it. Kio's home acts as a hub for the Catian visitors, and he frequently works alongside them and his human friends to resolve conflicts.

Throughout the series, Kio does not undergo a drastic personality shift, but he faces increasingly high-stakes situations. In the final episode, his development culminates in a significant physical transformation. When boarding the Catian mother ship to help his allies against an enemy force, he attempts to access the main computer. The computer denies his command because his DNA is off by a fraction of a percent from being a full Catian. To override this, he requests to become a Catian, and with the aid of a special bell, he is temporarily transformed into a cat-boy, complete with cat ears. While this change is temporary, it represents a final, complete merging of his human identity with the alien world he has come to defend.

Regarding notable abilities, Kio is not a superhuman fighter but possesses some practical skills. He knows how to handle firearms, a skill he has learned from his uncle, though the exact nature of his uncle's business that provides access to such weapons remains unclear to him. His most valuable ability, however, is his adaptability and his talent for forming cross-species bonds, which allows him to unite his human friends and the Catian aliens toward a common goal.