Takeshi Onimaru

Takeshi Onimaru is the main antagonist of the series and Yaiba's main rival. After mastering the Fuujin Sword he turned into a Oni because of Fuujin's possession, and was eventually fred by his influence at the end of the Yamata no Orochi arc.

Appearance
Onimaru is a tall but naturally bald and a serious expression, with a thin body frame. After turning into a Oni, he's become bulkier and taller, with a much more muscled body and small horns protunding from his forehead. As a student, he wore the typical black school uniform like the other male students. Before he was possessed by Oni and wearing his armor, he wore a white Japanese shirt and black hakama which is his Kendo uniform where he retrained himself to battle Yaiba.

In his demon form, Onimaru dons a fearsome elaborated armor with the breastplate shaped like a grinning skull, spiked shoulderpads and decorated greaves and bracers trimmed with black fur. He also wears a red cloak and occasionaly a black helmet shaped like a dragon's head. He also has a jetpack in the back of the armor. During the Oda Nobunaga tournament he wears a black kimono.

Personality
Onimaru is a very stern person, having no time nor patience for jokes. However, he's easy to anger and vengeful when provoked, seen when he tried to assault Yaiba in his sleep to take revenge for the former's joke. As a Oni, Takeshi is ruthless and power hungry, wanting to put the whole world under his command. He's not forgiving with his underlings, unless they're of use to him, like professor Kanabo. He despise weakness, but has still some honor. During the Yamata no Orochi arc he becomes even more ruthless and destructive than ever. After being turned back into his human form and his training with Kenjuuro, Onimaru's ambition and hate has been replaced with a pure, serene heart and now no longer fights for the sake of revenge.

Abilities
Even as a student, Onimaru was incredibly skilled at kendo, being capable of striking down a large man like Kumazawa with only one blow. After his transformation he can use the demon swords and has some magic power, as he can summon the Black Oni to do his bidding, hypnotize people and do other spells.

Weapons

 * Fuujin Sword ( 風神剣 Fuujin Ken) The sword of Fuujin, the God of Wind (also referred to as "The Devil of Wind), an ancient heirloom of the Onimaru family, kept in a dungeon under Onimaru's home. It has a long, single-edged blade with an oval, oblong guard and striped handle. There's a blue orb in the middle of the hilt. There's also a secret writing on the blade which can only be seen under moonlight. Thanks to this sword, Takeshi merged with Fuujin and became a Oni. He kept the blade as his weapon of choice during most of the series, and even though it was snapped in half during the Onimaru's Fortress Arc it was repaired. He eventually gave the sword to Yaiba during the Kaguya arc.
 * Devil King Sword ( 魔王剣 Maoken) The Devil King Sword is a fiendish weapon of incredible power forged by Kaguya and is the evil counterpart of the Supreme King Sword. It looks like a huge, double-edged longsword with a black blade and white borders. The handle is black and rectangular, and with a white tip. The hilt itself is composed by a round body shaped like a fiendish head (with the open mouth serving as a power gauge) and two horn-shaped arms protunding to the sides and adorned by what seems to be black fur. The blade of the weapon is slightly larger at the bottom and sports a hook near the hilt. This blade can turn the evil spirit of the user into energy blasts capable of erasing all life from the Earth. When fully unleashed the blade turns into black energy. This weapon is originally wielded by Gekko.
 * Fuurai Bazooka A bazooka that utilizes full powers of the Raijin Orb and Fuujin Orb to release a massive and destructive energy blast capable of destroying a planet.

Techniques

 * Fuujin Ha ( 風神 波 Wind God Wave) First used by Onimaru to defeat Yaiba on the school grounds, consist in a blast of wind shot from the sword's tip. It was named during the battle against Yaiba at the fortress.
 * Wind Blade: A variation of the Fuujin Ha and Onimaru's most common attack: a crescent shaped bullet of air capable of slashing through buildings.
 * Sorcery: Thanks to his status as a Oni, Onimaru can now use magic and sorcery, usually to turn helpless animals into humanoid demons to do his bidding.
 * Summon Black Oni: By throwing a handful of spikes and making a spell gesture, Onimaru can summon several Black Oni from the ground to act as his minions. He can seemingly summon an infinite number of servants this way.
 * Necromancy: Using spells similar to the ones used to create the demons, Onimaru can bring back to life ancient warriors and give them a beast-like body along with the possibility of taking human form.
 * Hypnosis: Thanks to his demonic powers, Onimaru can brainwash people with a glare. He first used this power to put the Japanese government in the Diet Palace under his control.
 * Tatsumaki Giri: (竜巻 斬り  Tornado Slash) Onimaru's trump card, developed under Kanabo's advice. Onimaru extends the arm holding the sword of Fuujin and spins on himself as he release more and more energy, creating a huge tornado which he then throws at his enemy like a drilling beam of energy. When first used was powerful enough to perforate Mount Fuji and rise as far as space.
 * Furaijinha ( 風 雷神 波 Thunder-Wind Gods Wave) A powerful combined attack powerful enough to pierce through a whole galaxy, it requires the combined energy of both the Raijin and Fujin Orbs to work. It was first used by Yaiba and Onimaru to defeat Gekko.
 * Yoko Ichimonji: A iaido technique which delivers and incredibly fast slash at the enemy with razor-sharp air, aimed at a vital spot. Onimaru first used this technique while fighting Yaiba on the Yamata no Orochi.
 * Tojin (闘刃 Battle Sword): An illusionary technique, in which the user summons his fighting spirit in the form of a flurry of invisible but discernable blades which distracts the enemy.

Detective Conan OVA: Conan vs. Kid vs. Yaiba
Onimaru made a briefly appearance in the crossover OVA, Onimaru has his oni minions shoot Yaiba and Kaitou Kid with a cannon during their mid-air battle.

Detective Conan
Main article: Takeshi Onimaru (Detective Conan)

Unlike his Yaiba counterpart, Onimaru never take the Fuujin Sword and turn into a demon in this series, as the Yaiba events are non-canon to Detective Conan universe. Also, Onimaru is voiced by Kenjiro Tsuda in Detective Conan anime instead of Ryo Horikawa.

In this series, Onimaru appears as an honorable, polite, and serious young man, albeit frightfully massive and skilled at Kendo. He apologizes to Ran when she runs headlong into his hard chest protector and winds up on the floor. He does not help her up though, and seems more concerned with refusing an honorary citizenship, which Momiji set up for him so he would leave the tournament so Heiji could win, he feels he does not deserve due to his a perceived lack of worthiness. Overall, his character appears to more purely embody a Makoto-type samurai mentality who likes fighting strong opponents. As he discusses the citizenship with the manager, he seems polite and even push a little laugh has both leave the hall.

Trivia

 * Takeshi Onimaru's name literally translates to "Fierce Demon".
 * Onimaru shared same voice actor with Heiji Hattori from Detective Conan, which is also drawn by Gosho Aoyama.
 * He bears a resemblance to Tenshinhan from the Dragon Ball series. His only difference is that he has a dot on his forehead instead of a literal third eye.
 * Onimaru's voice actor, Ryo Horikawa, is also voices Vegeta from Dragon Ball series.