LESSON NOTES · レッスンノート

N4What anime teaches · Oct 4, 2026

Demon in Japanese: 鬼おに (おに), 悪魔あくま (あくま) and the 魔王まおう of isekai

"Demon" in Japanese is usually 鬼おに (おに, oni) when you mean the horned demon of Japanese folklore, and 悪魔あくま (あくま, akuma) when you mean the devil or demon of Western religion and fantasy. Isekai anime adds a third: 魔王まおう (まおう), the Demon King.

English uses one word, "demon", for very different creatures. Japanese splits them, and anime translations then fold them back together, which is where the confusion starts. Demon Slayer fights 鬼おに. Chainsaw Man fights 悪魔あくま. The hero of a hundred isekai stories fights a 魔王まおう. All three come out as "demon" or "devil" in English subtitles. This post separates them, then shows the everyday side of 鬼おに, which is much bigger than monsters: a children's game, a February ritual, and a piece of slang you will hear from teenagers.

How do you say "demon" in Japanese?

What is a 鬼おに (oni)?

A 鬼おに is the demon of Japanese folklore: horns, wild hair, red or blue skin, a tiger-skin loincloth and a heavy iron club. It is less a symbol of pure evil and more a fearsome, powerful being from outside the human world.

昔むかし、この山やまには鬼おにが住すんでいた。 — Long ago, an oni lived on this mountain. (neutral, folktale opening) 桃太郎ももたろうは鬼おにを退治たいじしました。 — Momotaro defeated the oni. (polite, the famous children's story)

桃太郎ももたろう (ももたろう), the boy born from a peach, is the story every Japanese child knows, and his enemies are 鬼おに on Demon Island, 鬼おにヶ島しま (おにがしま). If you want a picture of an oni, that story is it.

What is 悪魔あくま (akuma)?

悪魔あくま is the devil or demon of the Bible and Western fantasy: Satan, demons that tempt people, contracts signed in blood. The kanji are 悪あく (bad, evil) and 魔ま (demon, magic).

悪魔あくまと契約けいやくする。 — To make a contract with a devil. (neutral, a classic fantasy setup) 彼かれは悪魔あくまのような笑顔えがおを見みせた。 — He showed a devilish smile. (neutral, written description)

Where 鬼おに is a creature from local folklore, 悪魔あくま is an imported idea, and it carries the moral weight of evil that 鬼おに often lacks. Dragons split in a similar way: the loanword ドラゴン is the winged European kind, while the 竜りゅう of folklore is a long wingless serpent of water and rain, and dragon in Japanese draws that line.

Which one does anime use?

It depends on the world of the story, and the English translation often hides the difference.

Title Japanese word What they are
鬼おに滅ほろの刃は (Demon Slayer) 鬼おに humans turned into man-eating oni
チェンソーマン (Chainsaw Man) 悪魔あくま devils born from human fears
はたらく魔王まおうさま! (The Devil Is a Part-Timer!) 魔王まおう a Demon King from another world
青あおの祓ふつ魔ま師し (Blue Exorcist) 悪魔あくま demons in a church-and-exorcist world

鬼おに滅ほろの刃は (きめつのやいば) is a good one to break down. 鬼おに is read き here, 滅めつ means "destroy", and 刃は is "blade". So the title is roughly "the blade that destroys demons", and the 鬼おに in it are the folklore kind.

Beyond the basics

What is a 魔王まおう?

魔王まおう (まおう) is the Demon King or Demon Lord, the final boss of fantasy games and the starting point of countless isekai plots. Around him are 魔族まぞく (まぞく), the demon race, and 魔物まもの (まもの), monsters.

勇者ゆうしゃは魔王まおうを倒たおすために旅たびに出でた。 — The hero set out on a journey to defeat the Demon King. (neutral, the classic RPG setup) 森もりには魔物まものがたくさんいる。 — There are many monsters in the forest. (neutral, fantasy setting)

The pair 勇者ゆうしゃ (ゆうしゃ, the hero) and 魔王まおう is so standard that many recent stories play with it: the Demon King who works part-time, the hero who retires, the 魔王まおう who turns out to be the nice one. More of the vocabulary gamers use is in Japanese gaming terms.

How is 妖怪ようかい different from a demon?

妖怪ようかい (ようかい) are supernatural creatures of Japanese folklore, and many of them are not evil at all. Some are mischievous, some are scary, some are simply strange: a talking umbrella, a water imp, a fox that changes shape.

この町まちには妖怪ようかいの話はなしがたくさんある。 — This town has many stories about yokai. (neutral, local legend)

So 鬼おに can be counted among 妖怪ようかい, but most 妖怪ようかい are not 鬼おに. If you watched ゲゲゲの鬼太郎きたろう or 妖怪ようかいウォッチ, you have met the friendly end of the 妖怪ようかい world. At the powerful end is the fox that changes shape, whose nine tails in 九尾きゅうびの狐きつね mark its strength, and fox in Japanese sets that legend beside the fox as messenger of Inari shrines.

Why do people say 鬼おに about real humans?

Because 鬼おに also means someone harsh, relentless or intensely devoted. This is the use you will actually hear in daily life.

あの先生せんせいは鬼おにだ。 — That teacher is a demon. (casual, complaining about someone strict) 部長ぶちょうは仕事しごとの鬼おにです。 — The department head is a work fiend. (polite, "devoted to work", half praise) 心こころを鬼おににして、子こどもを叱しかった。 — I hardened my heart and scolded my child. (neutral, being strict out of love)

鬼おにコーチ (おにコーチ) is a brutally strict coach. 心こころを鬼おににする, "make your heart into an oni", is a lovely phrase: being tough on someone for their own good.

What does 鬼おに mean in slang?

In young people's slang, 鬼おに in front of a word means "super" or "insanely".

このケーキ、鬼おにうまい! — This cake is insanely good! (very casual, young speakers) 今日きょうのテスト、鬼おにむずかった。 — Today's test was crazy hard. (very casual, むずかった = むずかしかった)

It is the same family as めっちゃ and すごく, just louder. Use it with friends only. Our post on very in Japanese puts all these intensifiers on one scale.

Where else does 鬼おに show up in daily life?

In a children's game, a February ritual and a word for a brat.

公園こうえんで鬼おにごっこをした。 — We played tag in the park. (casual, childhood memory) 鬼おには外そと!福ふくは内ない! — Demons out! Good luck in! (the chant of 節分せつぶん, shouted while throwing beans)

鬼おにごっこ (おにごっこ) is the game of tag, and the person who is "it" is called the 鬼おに. 節分せつぶん (せつぶん), in early February, is the day families throw roasted soybeans at someone wearing an oni mask to drive bad luck out of the house. And ガキ, the rough word for a kid or brat that anime characters love, comes from 餓鬼がき (がき), the "hungry ghost" of Buddhism.

What is a 小悪魔こあくま?

小悪魔こあくま (こあくま), "little devil", describes a playful, teasing person, usually a girl who is flirty and knows it. It is more compliment than insult in most contexts.

彼女かのじょは小悪魔こあくまっぽい。 — She's a bit of a little devil. (casual, teasing and charming)

In anime, the 小悪魔こあくま type is the character who teases the hero, then laughs when he gets flustered.

Common mistakes

  • Using 悪魔あくま for the oni of Japanese folklore. 桃太郎ももたろう fights 鬼おに, not 悪魔あくま. The images are completely different.
  • Calling a person 悪魔あくま casually. 悪魔あくま sounds truly evil. 鬼おに is the normal word for "a harsh person", and 小悪魔こあくま is the playful one.
  • Using 鬼おに slang at work. 鬼おにうまい is for friends. With anyone else, say とてもおいしい.
  • Reading 鬼おに滅めつ as おにめつ. In compounds 鬼おに is often read き: 鬼おに滅めつ (きめつ), 餓鬼がき (がき).
  • Treating every 妖怪ようかい as a demon. Many 妖怪ようかい are just strange or mischievous.

Quick comparison

Word Reading Meaning Feel
鬼おに おに oni, folklore demon; a harsh person Japanese, physical, fearsome
悪魔あくま あくま devil, Western demon evil, religious, contracts
魔王まおう まおう Demon King fantasy, games, isekai
魔物まもの まもの monster fantasy
妖怪ようかい ようかい yokai, supernatural creature folklore, not always evil
小悪魔こあくま こあくま little devil, teasing person playful, casual

Practice

Try each answer yourself before opening it. Questions 2 and 3 are a pair on the main contrast: folklore 鬼おに versus Western 悪魔あくま.

1. Which word is the demon fought in 鬼おに滅ほろの刃は?

Show answer

鬼おに — the title itself contains it, read き: 鬼おに滅めつ means "destroying demons".

2. A horned creature with red skin and an iron club, from a Japanese folktale. Which word?

Show answer

鬼おに (おに) — this is the oni of Japanese folklore, like the ones in 桃太郎ももたろう.

3. A being from the Bible who tempts people and makes contracts. Which word?

Show answer

悪魔あくま (あくま) — the Western devil. This is the pair to question 2.

4. Say "The hero defeated the Demon King."

Show answer

勇者ゆうしゃは魔王まおうを倒たおした — 勇者ゆうしゃ and 魔王まおう are the standard pair in fantasy and isekai.

5. Your coach is extremely strict. What casual word do you use about him?

Show answer

鬼おに (or 鬼おにコーチ) — 鬼おに describes a harsh person. 悪魔あくま would sound like he is truly evil.

6. What does 心こころを鬼おににする mean?

Show answer

to harden your heart and be strict for someone's good — literally "to make your heart an oni".

7. A friend says このラーメン、鬼おにうまい! What do they mean?

Show answer

This ramen is insanely good! — 鬼おに before a word is slang for "super". Friends only.

8. What is the Japanese name for the game of tag, and what is the "it" person called?

Show answer

鬼おにごっこ, and the "it" person is the 鬼おに — the chaser plays the demon.

9. What do people shout while throwing beans on 節分せつぶん?

Show answer

鬼おには外そと!福ふくは内ない! — "Demons out! Good luck in!"

10. Which word describes a teasing, flirty "little devil", usually as a half-compliment?

Show answer

小悪魔こあくま (こあくま) — playful, not evil. Compare it with 悪魔あくま, which is genuinely dark.

Explain in a trial lesson why the villain of your favourite series is 悪魔あくま and not 鬼おに, and where 魔王まおう fits in isekai.

FAQ

Is "oni" the same as "demon"? Close, but not exact. "Demon" is the usual English translation, yet an oni is a specific creature of Japanese folklore. Some people prefer "ogre" or simply "oni".

What is the Japanese word for "devil"? 悪魔あくま (あくま). For Satan himself, the katakana サタン is also used.

How do you say "demon slayer" in Japanese? The anime's title is 鬼おに滅ほろの刃は (きめつのやいば). The members of the Demon Slayer Corps are called 鬼おに殺さつ隊たい (きさつたい), and a member is a 隊士たいし (たいし).

Is calling someone 鬼おに rude? It is blunt, but usually it is a complaint about strictness, not a real insult. Said to their face, it can sting, so read the room.

What is デーモン? The katakana loanword for "demon". It appears in game and fantasy titles, but in everyday speech 悪魔あくま is far more common.

What does 鬼門きもん mean? 鬼門きもん (きもん) is the "demon gate", the unlucky northeast direction in traditional belief. Figuratively it means someone's weak spot: 数学すうがくは私わたしの鬼門きもんです, "Math is my nemesis."

Vocabulary from this article

Tap the block to select all of it, then copy. In Anki: File → Import, note type Basic, separator Tab — the first column becomes the front, the second the back.

鬼	おに — oni, demon of Japanese folklore; a harsh person
悪魔	あくま — devil, Western demon
魔王	まおう — Demon King
魔族	まぞく — demon race (fantasy)
魔物	まもの — monster
妖怪	ようかい — yokai, supernatural creature
勇者	ゆうしゃ — hero (fantasy)
小悪魔	こあくま — little devil, teasing person
鬼ごっこ	おにごっこ — the game of tag
節分	せつぶん — bean-throwing festival in early February
鬼ヶ島	おにがしま — Demon Island
心を鬼にする	こころをおににする — to harden your heart (for someone's good)
餓鬼	がき — hungry ghost; origin of ガキ (brat)
鬼門	きもん — unlucky direction; someone's weak spot
契約	けいやく — contract
退治	たいじ — defeating, exterminating (monsters)

I'm Yuuki, a Japanese teacher based in Tokyo. I've taught on italki as a Top 1% teacher and watched over 1,500 anime, so most of the example sentences on this blog come from lines I've actually heard students ask about. Demon Slayer and isekai titles bring up this exact question in lessons: why is everything "demon" in English? For practice with feedback, Book a trial lesson · $13, or work through Japanese practice exercises first.

Sources: the author's own lessons; standard Japanese dictionaries; the official Japanese titles of the series mentioned.

More drills like the ones above, plus a timed JLPT-style mock test: Practice · N4 · Read something at this level: JLPT N4 stories with audio

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