The 5th strongest of the Jyūshinshu and wears Hyōma En on his right hand in a pata sword fashion. He is called by Kurei as a lone wolf, but clearly is respected by the latter, as is seen when Kurei orders Mikoto not to speak a single word against Kai after his death.
During his first appearances, Kai wore a dark green cloak, concealing his body and face. Underneath it, Kai is a tall, muscular man who wears his black hair in thick dreadlocks (similar to reggae singer Bob Marley). In a flashback, he was seen wearing the traditional outfit of a swordsman. He also wore earrings.
Kai is one of the most determined characters in the entire series. His attempts at bettering his skills are the defining trait of his character. Kai is also full of pride and refuses to believe a swordsman ten years younger than himself could be superior. In his flashbacks it is seen that he is hard working and firmly believes that hard work and unending dedication to swordsmanship can overpower the talent of a genius such as Tokiya. During his training in the art of Hyomon Ken, he was constantly reminded by Meguri Kyoza that Tokiya did everything Kai did, and he did it with perfection, while Kai was inferior. He was also passionate enough about winning over Tokiya that he shed a tear in joy. This constant goading pushed him to master Hyomon Ken in only one year, while it took Tokiya seven years. Despite using such a bloodthirsty madogu, Kai himself is honorable enough to pause a battle in order to allow Tokiya to pick up his weapon, and will not strike down a defenseless opponent.
Part in story
Kai studied Hyōmon Ken under Meguri Kyōza, who also trained Mikagami. Through constantly comparing him to his senpai Mikagami by saying that Mikagami is "gold" and he is "a rock", Meguri Kyōza instilled within Kai a sense of anger and revenge in order to show Mikagami how futile living his life only for revenge is. Kai battles against Mikagami in the final round of the tournament and manages to defeat him, fulfilling his desire to be the best Hyōmon Ken master and in order to avenge his broken pride. After telling Mikagami not to live a life of revenge the way he himself did and that it was Meguri Kyōza who killed Mifuyu, Kai stabs himself with the Hyōma En to feed its thirst and allows himself to fall into the pit below the arena. In the anime, Kai is supposedly the first Hyōmon Ken successor, but is discarded soon after Meguri Kyōza noticed Mikagami's potential. He also says that Meguri Kyōza killed Mifuyu, but adds that Meguri Kyōza's reason for doing so is because he believed that revenge would drive Mikagami to train harder (he says nothing about Meguri Kyōza's motives in the manga). After his battle with Mikagami, he does not stab himself with the Hyōma En, but he still allows himself to fall into the pit.
Hyōma En & Hyōmon Ken
Kai wields the Madōgu Hyōma En, which can manipulate ice and is the evil counterpart of Tokiya Mikagami's Ensui. In the manga, the Hyōma En has a mind of its own and constantly demands to be fed blood, especially Mikagami's. He is able to take ice from moisture in the atmosphere using Hyōma En to continue to use his ice based attacks.
Kai is an expert swordsman that was taught the Hyōmon Ken by Meguri Kyōza.