Kaito is first introduced as a seasoned, high-ranking Hunter and a former student of Gon Freecss's father, Ging. When he encounters a young Gon on Whale Island, Kaito saves the boy from a foxbear attack. Recognizing him as Ging's son, Kaito reveals that Gon's father is still alive and was a Hunter, not dead as Gon had been led to believe. This revelation ignites Gon's own journey to become a Hunter. Kaito leaves Ging's Hunter License with Gon as a clue, describing the search for his elusive master as the most difficult hunt in the world. Kaito's primary profession is discovering and documenting new animal species, a job that often takes him to remote locations with a team of fellow Hunters.

Kaito possesses a calm and stoic personality, often appearing blunt or even severe. This trait is evident when he strikes young Gon for his recklessness, which led to the foxbear's death, and when he later scolds Gon for showing sympathy towards aggressive Chimera Ants. Beneath this stern exterior, however, he is deeply caring and protective, especially towards Gon and his friend Killua. He values life but does not hesitate when taking it becomes necessary, a pragmatic philosophy that guides his actions. A keen analyst, he often makes sharp observations about his opponents and situations, demonstrating a deep understanding of combat and strategy.

Kaito's relationship with his master, Ging, is foundational. Ging saved Kaito from a life on the streets, and Kaito seeks to repay that debt by proving his worth, though he also shows frustration and bewilderment at Ging's elusive nature. His connection with Gon is paternal and instructive; he acts as a mentor who provides the boy with his life-defining goal and later watches over his growth. When they reunite during the Chimera Ant crisis, Kaito takes on the role of a leader, guiding Gon and Killua through the dangerous mission.

During the Chimera Ant arc, Kaito infiltrates the autonomous nation of NGL to investigate and stop the threat of the rapidly evolving Chimera Ants. This arc defines his role as a courageous and skilled fighter. In a tragic turn, he is killed while protecting Gon and Killua from the powerful Royal Guard Neferpitou. After his death, Neferpitou reanimates and manipulates Kaito's corpse, using it as a training puppet. Kaito's fate takes an unexpected turn when it is later revealed that he has been reincarnated as a small, red-haired girl born from the Chimera Ant Queen. This new being retains Kaito's memories and identity, insisting on being called by his original name. It is implied that this rebirth was made possible by one of the abilities of his Nen weapon.

Kaito's most notable ability is his Nen technique, Crazy Slot, a conjuration ability. He manifests a large, numbered clown-faced roulette wheel that randomly selects a weapon, typically ranging from one to nine. To make the conjured weapon disappear, Kaito must use it at least once. This random nature is a self-imposed restriction that greatly increases the power of the weapon drawn, though Kaito often complains loudly when he gets a result he finds undesirable. Among the known weapons are a giant scythe for a devastating area-of-effect attack called Silent Waltz, a rifle, and a mace. A specific, rare number on the roulette conjures a simple clown doll or baby rattle, which is believed to be the ability that facilitated his reincarnation after his death. Beyond his conjured arsenal, Kaito is also a highly skilled combatant with strong fundamental Nen abilities, fine-tuned under Ging's tutelage, and possesses an innate affinity for animals. His development from a mysterious mentor figure to a tragic casualty of war and finally to a mysteriously reincarnated being underscores his resilience and the profound impact he has on the story's central characters.