[[quoteright:232:https://static.tvtropes.org/pmwiki/pub/images/ogreslayer.jpg]]

''Ogre Slayer'' (鬼切丸 ''Onikirimaru'') is a manga series created by Creator/KeiKusunoki. The manga has been adapted into a 4 episode OAV which was the first production of Creator/OLMIncorporated. 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

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!!This series contains examples of:

* AbsurdlySharpBlade: Onikirimaru, who usually has no problems slicing through ogres.
* AsLongAsThereIsEvil: The Oni in the third episode of the OVA taunts Ogre Slayer with this line during their fight, telling him that it doesn't matter how many Oni he kills. Humans can become or give birth to new Oni, so as long as the human race exists so will Oni to feed upon it.
* AssholeVictim: The series has a lot of horror elements and often the first victims of a story are people who are abusive to their servants, bandits, or in modern Japan, JapaneseDelinquents and gangsters.
* 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.]]
* BitterSweetEnding: Onikirimaru can’t save everyone and some of the characters are their own worst enemies or they get in over their heads. Generally at the end of each story, only 1 or 2 of the characters is still alive by the time the Oni has been slain.
* 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.
* ChildEater: Many Oni are all too happy to dine on the flesh of humans, regardless of age. [[spoiler: The Oni in the third episode of the OVA even ''specializes'' in this. He grants children to the women who pray at his shrine, but then forces the child's own mother to kill them on their 5th birthday so that he can devour them. We even get to see him do this onscreen to his first victim!]]
* ClothingDamage: To an almost absurd degree. The first three episodes of the OVA ''all'' open up with a young woman being stalked and attacked, resulting in their shirts coming apart and leaving them wholly or partially naked. The fourth and final episode is the only one that starts differently... and only because it involves an Oni massacre instead.
* CoolSword: Onikirimaru, one of the few things that can surely kill an ogre.
* CreepyChild: Many stories have teenagers possessed by an Oni or were raped and are carrying an Oni child. There are other stories of Oni being born from incestuous relationships. [[spoiler: The Oni in the chapter "Tag" is revealed to be an Oni that looks like a child but is implied to be over 50 years old. The Oni eats anyone who 'loses' tag to him. It is implied he may have killed his whole family off due to his mother's incestuous relationship with her brother.]]
* DarkerAndEdgier: The [=OVA=] compared to the manga.
* DealWithTheDevil: Some of the Oni will offer some form of bargain to their potential victims that royally screws them over in the end. One great example of this is the villain of episode 3 of the OVA who offered infertile human women the chance to conceive if they prayed at a certain shrine. The catch? [[spoiler: They have to then murder their own child on their 5th birthday so that the Oni can feed on it!]]
* DemonicPossession : Oni are frequently shown to have the power to overshadow humans and take refuge inside their bodies. Oftentimes the only way to stop said Oni is for Ogre Slayer to kill the unfortunate human host.
* 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.
* {{Foil}}: In Onikirimaru-den, Suzuka Gozen and Onikirimaru are this. [[spoiler: Onikirimaru was born out of a nun, devoured by Shutten Douji and hates humanity because he feels they didn't help his human mother, but will still slay demons because they killed his mother. Suzuka Gozen was a demon who fell in love with a human, gave birth to a human child and loves humanity. In their encounter, Suzuka tells Onikirimaru that she shall observe him until he loves humanity and desire to become human, which by present day, he does.]]
* {{Gorn}}: Borders on {{Narm}} at times.
* HeroicSacrifice: Many of Ogre Slayer's allies have been forced to do this to stop or undo some of the damage caused by that story's Oni. [[spoiler: The protagonist of the first episode of the OVA lets Ogre Slayer cut her down to finish off the Oni she brought into the world and the mother in episode three offers up her own life to revive her dead child.]]
* HeWhoFightsMonsters: This is the FatalFlaw of the protagonist of the first episode of the OVA. After being constantly bullied by her peers she sees the Oni possessing her as a blessing since she thinks they protect her from danger and only kill people who deserve it. [[spoiler: It isn't until they remorselessly slay her best friend that she realizes that they're just cruel monsters that she's unleashed on the world for her own benefit. The episode ends with her sacrificing herself so that the Oni can finally be destroyed, realizing that she became a part of the very problem she was trying to fix.]]
* HumansAreBastards: Ogres are not the only ones doing evil deeds in the world; in fact, some of the evil deeds humans do end up giving up birth to Ogres.
* HunterOfHisOwnKind: Onikirimaru, born out of an Ogre, hunts Ogres. [[spoiler: This is actually revealed to not be entirely the case in the sequel series.]]
* 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.
* KnightErrant: Onikirimaru is basically this, wandering the land and slaying any Oni he encounters or his sword alerts him to. Interestingly enough, most Oni know who he is once he attacks or appears before them, often mocking his desire to be human. Despite most Oni not keeping in contact with one another, they seem to have a strong word of mouth with regards to Onikirimaru's mission.
* 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, by default, specially given he's the protagonist
** 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, a demon princess that became sorta-human after falling in love with one and giving birth to his child. She also fights demons because she loves humanity.
* NotSoDifferentRemark: Onikirimaru does remark this about himself and Ryoko; he also remarks this about some humans and ogres.
* OlderThanTheyLook: Onikirimaru, being several hundred years old.
** [[spoiler: The main villain in one chapter is a child who is really at least 50 years old. His own mother had him due to an incestuous relationship with her brother.]]
* Oni: The main antagonists of the story.
** OurDemonsAreDifferent: The Oni seen in the manga cover their wide history of different mythologies and urban legends. Some oni are spirits that possess humans to get a body. They can have a wide variety of mystical powers, be spirits, and be alive at the same time. Humans will turn into Oni if they are possessed, feel intense hatred for others, or make a deal with an Oni.
* 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, again, being actually born during feudal japan.
* {{Retcon}}: Onikirimaru-den, the prequel, [[spoiler: changes Onikirimaru's origin 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, both tend to smile
* TakesOneToKillOne: He is a pure-blood ogre, despite his looks. [[spoiler:Later retconned.]]
* TallDarkAndHandsome: Onikirimaru, given his origin and his goal.
** TallDarkAndSnarky: He's also a bit of an ass, but it's kind of warranted.
* 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, who actually seeks to end ogres, so he can become human and die.
* WildCard: [[spoiler: Suzuka Gozen, an actual female demon that loves humanity.]]

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