Takeshi Onimaru

Onimaru is disciplined, proud, serious, and intensely competitive. Unlike Yaiba's carefree approach to fighting, Onimaru values structured training and initially regards Yaiba's wild behavior as insulting.

His pride makes defeat particularly difficult for him to accept. Yaiba's ability to challenge him despite lacking conventional discipline transforms their disagreement into a fierce rivalry.

Even when positioned as Yaiba's enemy, Onimaru retains the mentality of a martial artist. Strength, improvement, and proving himself against worthy opponents remain central to his decisions.

Onimaru is an exceptional swordsman even without supernatural assistance. His kendo ability places him among the strongest young martial artists associated with Gosho Aoyama's works.

In Yaiba, Onimaru obtains the Wind God's Sword and is possessed by its corrupting power. The transformation gives him demonic features and greatly increases his strength while allowing him to unleash destructive wind-based sword techniques.

He commands supernatural servants and develops increasingly powerful techniques as his conflict with Yaiba escalates.

In Detective Conan, his abilities remain grounded in extraordinary kendo skill rather than overt supernatural powers.

Onimaru meets Yaiba as a fellow young swordsman and rapidly becomes his principal rival. Their conflict escalates after Yaiba humiliates him and Onimaru seeks greater strength.

The Wind God's Sword transforms Onimaru into a demon and drives him toward conquest, leading him to build an army and send the Eight Demons against Yaiba. Yaiba's acquisition of the Thunder God's Sword establishes the opposing supernatural forces around which their conflict develops.

Later threats force Yaiba and Onimaru to cooperate despite their rivalry, demonstrating that Onimaru's role is more complicated than that of an unchanging enemy.

Within Detective Conan, Onimaru appears as a famous high-level kendo competitor whose tournament performances intersect with Heiji.

Yaiba Kurogane is Onimaru's principal rival. Their mutual determination to surpass one another drives much of Yaiba's conflict, while [later threats occasionally force Yaiba Kurogane and Onimaru to fight together.](#spoiler)

Heiji Hattori knows Onimaru through competitive kendo and regards him as an exceptionally dangerous opponent.

Gerozaimon Geroda initially serves Onimaru as one of the Eight Demons. After Gerozaimon repeatedly fails against Yaiba, Onimaru abandons him and Gerozaimon changes sides.

Ayame Onimaru is Onimaru's younger sister.