The young Chief of the Fūma Ninja clan, who works for the Hojo clan. Kotarō Fūma (風魔 小太郎 Fūma Kotarō) confounds his opponent with his agile movement and countless Ninjutsu. His childhood has been stained by the experience of being abandoned by his mother; which has caused him to distrust women. However, it is wiped by Oyu's caring and kindness. He appear to be in his late teens to early twenties. He is introduced after Jubei escapes Gifu Castle with Oyu, but can be found earlier in the story at the top of the inn, after talking to some villagers in Imasho. He warns Jubei to beware of Oyu, and not to trust her.
When Jubei finds himself lost in a forest, Kotaro comes to his rescue after impersonating Jujudormah.
In the Oni's Sacred Place, Kotaro confronts Oyu and accuses of her of being a spy for the Oda Clan. He then warns her to stay away from Jubei, or else. When she refuses to, he tries to kill her, but is knocked aside by a demon. As he is about to be killed, Oyu saves him and then tries to help, when he refuses her help. Oyu then inquires Kotaro about his past, thinking that his mother did not truly abandon him. Upset, he tells her to be quiet, and then flees.
Near the end of the story in one of the endings, when Jubei faces Ginghamphatts for the third and final time, Oyu arrives to help him. However, she is knocked aside by Ginghamphatts, and almost falls to her death, until she is rescued by Kotaro. But then Kotaro is stabbed in the back by Ginghamphatts, and falls to the ground, dying. Seeing this, Jubei flies into a rage and kills Ginghamphatts, once and for all. As he lies on the ground dying, Kotaro finally reveals his past to Oyu. He wasn't abandoned by his mother, but she was trying to escape Fuma Village with him when he was a child, so he would not have to become a ninja and put his life on the line. The ninja of the village hunted them down, and killed Kotaro's mother, leaving him alone, which explains why he said she abandoned him. He then apologizes to Oyu for how he acted, and then dies in her arms, while remembering his mother.
- The character was based on the historical ninja of the same name.
- It can be assumed that his death in Onimusha 2: Samurai's Destiny is non-canonical, for he appears in Onimusha: Tactics and in Onimusha Blade Warriors, the latter which takes place a few months after Onimusha 2, and 11 years before Onimusha 3.