''Ogre Slayer'' (鬼切丸 ''Onikirimaru'') is a manga series created by Kei Kusunoki. The manga has been adapted into a 4 episode OAV. A prequel, ''Legend of Ogre Slayer (''Onikirimaru-Den''), set in medieval Japan, is currently being released, by the same creator.

''Ogre Slayer'' is about a young man who hunts ogres. The young man was born of an ogre's corpse, like the oni born of human's body, making him pure ogre blood. Though he was born like an ogre, he has the appearance of a human. Instead of being born with horns like traditional Japanese ogres, he was born with a sword. The young man doesn't have a name, but his sword is called Onikirimaru, the Ogre Slayer.

Note: In original language Ogre is "Oni", demons of Japan tradition

!!This series contains examples of:

* AbsurdlySharpBlade: Onikirimaru
* BecomingTheMask: [[spoiler: He calls himself a demon, and is happy to continue spreading the rumor that he was [[MetaphoricallyTrue born out of one]], even though his {{retcon}} origin is that he was sent by the gods themselves. Of course, he also absorbed the demon's essence during his birth so he's kinda a demon in that way.]]
* BeenThereShapedHistory: Onikirimaru, in the prequel/sequel.
* BornLucky: One of the Ogre hosts has escaped many accidents unhurt, turns out it's because the ogre is just protecting it's host.
* CoolSword: Onikirimaru, one of the few things that can surely kill an ogre.
* DarkerAndEdgier: The [=OVA=] compared to the manga.
* EmpathicWeapon: Onikirimaru won't hurt the nameless hero as it's actually part of him.
* EquivalentExchange: Some of the ogres will grant a human a wish, it's not until later when they realize the price they have to pay for it.
* {{Gorn}}: Borders in {{Narm}} at times.
* HumansAreBastards
* HunterOfHisOwnKind
* IJustWantToBeNormal: Onikirimaru, whose quest to kill all of his kind is done in the belief that once he completes this nigh impossible task, he will become human, get a name of his own and live a normal life.
* KickTheDog: Ryoko, the maid, get's constantly abused by the rich family she serves.
* TheNameless: The main character has no name, but is referred to by the name of his sword as a placeholder.
* TheMessiah: [[spoiler:Onikirimaru-Den reveals that he's a child of the gods, sent to earth thru a MysticalPregnancy, in order to protect humanity from the demons.]]
** DarkMessiah: [[spoiler: However, because men tasked with protecting her mother failed, he harbors resentment towards humanity.]]
* MetaphoricallyTrue: [[spoiler: Onikirimaru was actually born from a [[MysticalPregnancy nun]] that had been devoured by the demon Shutten Douji, but in the process of being born, he absorbed Shutten Douji's essence and burst out from the demon itself, giving the impression he was born from a demon.]]
* NobleDemon: Onikirimaru. Benkei, a demon loyal to Minamoto no Yoshitsune, who fought against an army in order to give his master time to commit seppuku undisturbed. Suzuka Gozen.
* NotSoDifferent: Onikirimaru and Ryoko; conversely, some humans and the ogres.
* OlderThanTheyLook: Onikirimaru.
* OnlyKnownByTheirNickname: The nameless hero is most commonly known as Onikirimaru, which is the name of his sword.
** IAmNotShazam
* PetTheDog: Onikirimaru to Ryoko, the maid.
* ReallySevenHundredYearsOld: Onikirimaru.
* {{Retcon}}: Onikirimaru-den, the prequel, [[spoiler:changes the background as to be a child of the gods. The demon Shuten Douji devoured his mother, while he was still in her womb; during the process, he absorbs Shuten Douji's essence and bursts out from his insides, sword in hand, killing him.]]
* SealedEvilInACan: Some ogres start the stories this way; Onikirimaru unseals them himself so they can be properly slain.
* StepfordSmiler: Ryoko, and Onikirimaru.
* TakesOneToKillOne: He is a pure blood ogre, despite his looks.
* TallDarkAndHandsome: Onikirimaru.
** TallDarkAndSnarky
* TooDumbToLive: Some of the ogre victims.
* TooGoodForThisSinfulEarth: [[spoiler: Ryoko in the original series. Onikirimaru's mother in the prequel/sequel.]]
* UrbanLegend: Younger people think Onikirimaru is just a legend.
* WalkingTheEarth: His endless quest to finish off all ogres.
* WhoWantsToLiveForever: Onikirimaru
* WildCard: [[spoiler: Suzuka Gozen, an actual female demon that loves humanity.]]