Onimaru is the primary antagonist of Yaiba. Originally a gifted high school swordsman, he was humiliated by Yaiba who attempted to challenge him and eventually they became bitter rivals. Obsessed with beating Yaiba, Onimaru discovered in a secret cellar of his house the Legendary Fujin Sword, and attempted to master it, turning himself into a powerful and large Oni bent on killing Yaiba and conquering the whole World.
He later came into conflict with Kaguya the Moon Empress, who also sought to take over Earth and during a 24-hour war, he was trapped in Kaguya's frozen carbon. Freed by Yaiba, Onimaru unwillingly teamed up with him against Kaguya's strongest henchman Gekko, who possessed the Demon King Sword of terrifying power. After Yaiba defeated Kaguya and sealed her into the Earth's core, Onimaru, now armed with the Demon King Sword he took from Gekko, went into hiding.
Onimaru later tricked the People of the Underworld into establishing an alliance and had them using their Pyramids to attack the surface world. Yaiba and his group arrived in the Underworld hoping to stop them, but were attacked by two biological cyclops robots named Gold and Silver that were created under Onimaru's advice. Onimaru then revealed his plan of destroying both the Underworld and the surface world using Gold, who he helped evolve into an oni using the Demon King Sword's demonic ability. However, Gold was later killed by Yaiba, and the Underworld people withdrew all the pyramids.
Onimaru later succeeded in finding and destroying the 8 swords that seal the powerful Yamata no Orochi, who he used to conquer Earth. The Yamata no Orochi was however defeated by the combined efforts of Yaiba and a Kaguya-possessed Sayaka. Yaiba defeated Onimaru and cut off his oni horns, freeing him from the demon once and for all.
Powers and Stats
Tier: 9-C | 8-B, 7-A with Tornado Slash | Likely 5-B | 8-A with weakest attacks, 5-B with Full-Moon Slash | 9-A
Name: Onimaru Takeshi
Age: 15 in Nobunaga Tournament Arc, 18 at the end of story
Classification: Human, Swordsman, Oni, Fuujin incarnation
Powers and Abilities: Peak Human, Swordsmanship | Same as base but increased to superhuman levels, Wind Manipulation, Energy attacks, Mind Control, Summoning black oni, Necromancy | Planetary-scale destructive Energy blast | Superhuman Physical Characteristics, Swordsmanship, Energy Manipulation | Same as base but to a much higher degree
Attack Potency: Street level | City Block level with Wind God Wave (Demolished a skyscraper), Mountain level with Tornado Slash (Drilled through the Earth's surface) | Likely Planet level (Destroyed what appeared to be Saturn, but given the author's sense of scaling, this should likely be treated as a normal planet) | At least Multi-City Block level with weakest attacks, Planet level with Full-Moon Slash | Small Building level (The impact of his bokken clashed with Yaiba's destroyed a flaming replica of Honnō-ji)
Speed: Subsonic (Barely dodged an arrow at extremely close range) | Unknown. Possibly Massively Hypersonic (Dodged Yaiba's lightning blast at close range) | Unknown combat speed. Possibly Massively FTL attack speed (Reached what appeared to be Saturn in seconds, but given that Yaiba and Gekko dodged this attack, it may be an Outlier) | Unknown. Either Massively Hypersonic+ or FTL (Fought Yaiba wielding the Haou-ken, but Yaiba's speed during this arc is very inconsistent) | Likely Supersonic+ (Fought equally with Yaiba)
Lifting Strength: Unknown
Striking Strength: Street Class | City Block Class | Unknown | Likely Planet Class | Small Building Class (Destroyed a flaming replica of Honnō-ji with the shockwaves from his bokken clashing with Yaiba's)
Durability: Street level | Unknown due to inconsistency (Was at the epicenter of an island-sized explosion, and later also survived a blast from True Form Kaguya. However, in the same arc he was also injured by Kaguya's weaker rabbit head, as well as a natural lightning) | Unknown | Unknown, possibly Planet level at his peak (Took attacks from Yaiba's fully powered Haou-ken, which sliced his planet-busting Full-Moon Slash) | Small Building level
Stamina: Extremely high
Range: Extended melee range with swords; hundreds to thousands of meters with energy attacks
Fujin Sword (風神剣): The Sword of Fuujin, the God of Wind, an ancient heirloom of the Onimaru family, kept in a dungeon under Onimaru's home. Thanks to this sword, Takeshi merged with Fuujin and became an 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.
Demon King Sword (魔王剣 Maoken): A fiendish weapon of incredible power forged by Kaguya and is the evil counterpart of the Supreme King Sword. 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.
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.
Intelligence: Skilled combatant. Once possessed by Fuujin he proved to be a very intelligent strategist, having Spiderman finding out Kaguya’s weaknesses before fighting her, outlining a plan to prolong the battle against Kaguya until she ran out of extract, and tricking the people of the Underworld.
Weaknesses: Overconfidence and normal human weaknesses | Onimaru loses all his oni powers once his horns are cut off. He cannot fly without his jet-pack | The Fuurai Bazooka can only be used once due to massive power output | The power of the Maou-ken is dependent on his dark evil spirit | None notable. He has turned back into a human again, but due to intense training his normal human physical and psychological weaknesses are greatly reduced.
- 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.
- 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 releases 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 that requires the combined energy of both the Raijin and Fujin Orbs to work. It was first used by Yaiba and Onimaru to defeat Gekko.
- Crescent Slash: The Maou-ken’s weakest special attack. It resembles the Wind Blade in appearance, only black in colour and more powerful in destructive capacity. This attack can easily destroy one of the 8 heads of a dragon the size of Japan.
- Half-Moon Slash: The Maou-ken’s second strongest attack. Onimaru concentrates more dark energy into a giant dark sphere which he then throws at his enemy. This attack can easily destroy an island, making an explosion that can be seen from the atmosphere.
- Full-Moon Slash: The Maou-ken’s strongest attack, capable of destroying a planet in an instant (image). This attack is similar to the Half-Moon Slash, only lighter in colour and much more powerful.
- Yoko Ichimonji: An 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.
Key: With Shinai (as a human) | With Fuujin-ken | With Fuurai Bazooka | With Maou-ken | Oda Nobunaga Tournament Onimaru (human) with Bokken
Note: The author's sense of power scaling made it nearly impossible to ascertain Takeshi's durability and speed.