"Kyoken no Izayoi" (lit. Izayoi of the Mad Sword) is a swordswoman of Yami's Armed Division.
As with most of Yami's women, Izayoi has cast aside her femininity, to the point where she feels nothing when her breasts are revealed, as long as her opponent loses. However, upon realizing Kensei's true purpose for stripping her armor, she felt sorry for having to kill him and wished to have met him sooner in life, apparently being one of few females, if not the only one, to have actually fallen for him.
When Akisame Kōetsuji and Kensei Ma arrive in Yami's American base in Okinawa, they meet Izayoi and the Spear of the East, and agree to take them on respectively as suiting their own styles. However, Kensei finds out that Izayoi is a girl, and desires to use his "Ma-style Restriction Technique" on her, ends up challenging Akisame to Janken, resulting in the temporary immobilization of one of his arms as he fights Izayoi.
This disadvantage seems to have been taken advantage of by Izayoi, who wounds the Chinese Kempo master several times until Ma reveals that he had taken her undergarments from beneath her clothes. This irritates her to the point where she takes off her armor and freely reveals her breasts, resolving to defeat Ma with the advantage of having to carry less weight. However, Ma effortlessly breaks her helmet in half and drapes his robe around her shoulders, saying that he aimed not to break her physical armor, but to break the armor around her heart. This touches Izayoi, who seems to apologize and even feel sorry that she would have to kill Ma during the lockdown. However, Ma manages to prevent this by slamming Izayoi against the wall with a left-hand strike, forcing the swordswoman to recognize the Kempo master's hidden strength and coming to terms with her attraction towards him, wondering what would have happened if she had met him sooner. Her sword, which flies through the air, is subsequently broken by Ma.
Master Swordswoman: Izayoi is exceptionally skilled in swordsmanship where she is capable of challenging Kensei Ma of Ryozanpaku with the Chinese martial artist having difficulties against her initially due to his incapacitated right arm. Her favorite technique of the sword involved swinging it madly around her in circular motions for an omnidirectional attack that gave her the epithet "Izayoi of the Mad Sword" and the Spear of the East of the Spears of Kurokonoe vouching for her skills as well.Enhanced Speed and Reflexes: Izayoi is shown to be fast enough to contend with Kensei Ma, the Ryozanpaku master known for his great speed especially when facing a woman, in speed. The Chinese master even had some difficulties against her due to both his injured right arm and the indiscriminate directions of where she swung her sword at. However he stilled managed to outpace her in multiple instances after getting used to her attacks as he was able steal her clothes and undergarments underneath her armor without her noticing it.
- Her name Izayoi means "sixteen-day-old moon" in Japanese. A sixteen-day-old moon has just passed its fullest phase, so it is at this point that its brightness begins to decline.