Blue Oni Red Oni

In anime, when oni 鬼 characters are involved, it's common for there to be a blue oni and a red oni, the blue oni having a single horn and the red oni two horns.

Goz, ゴズ, and Mez, メズ, a pair of a blue and a red oni 鬼, facing Son Gokū 孫悟空.

Left: Goz, ゴズ
Middle: Mez, メズ
Right: Son Gokū 孫悟空
Anime: Dragon Ball Z, ドラゴンボールＺ (Episode 13)

The origin of this blue oni red oni trope comes from a certain children's tale about friendship. It was a popular one, so references to it spread across all media and fiction, not just anime.

Note that, most of the time, there's usually no deeper meaning to the red oni blue oni combo. It's simply that if there's a red oni, the blue oni will show up sometime, or vice-versa.

Story

The Japanese Wikipedia has a version of the story^{(wikipedia:泣いた赤鬼)} that I'll talk about here. There are multiple variations of the tale, but the gist of it is usually the same.

Skip to the transcript if you want to read the story and don't want to be spoiled by the summary and moral.

Spoiler Summary

In the story, a red oni tries to become friends with humans, but oni, being scary, scare humans away, so not a single human comes by to play with him. He then asks his friend, the blue oni, for help. The blue oni comes up with a plan: he'd attack the human village, play the evil oni, and then red oni would fend him off, saving the humans, and becoming acknowledged as a hero oni. Doing this, the red oni becomes friends with humans, and plays with them every day. But for some reason his old friend, the blue oni, doesn't show up to play with him any more. Later he gets a letter from the blue oni, which tells if he came to play the humans would think they're friends, and then the whole plan would fall apart, so he wouldn't come play anymore. The story ends with the red oni crying for having lost his old friend.

Spoiler Moral

If I had to guess the moral, I'd say it is: do not lose your current friends to get new friends. Which is a common theme in fiction, and in anime, where you have characters who cut ties with their old friends of infancy in order to start hanging with the cool kids group, often regrettably.

Transcript

toaru yama no naka ni, hitori no aka oni ga sunde-ita. aka-oni wa zutto ningen to nakayoku naritai to omotte-ita.
とある山の中に、一人の赤鬼が住んでいた。赤鬼はずっと人間と仲良くなりたいと思っていた。
Inside a certain mountain, one red oni lived. The red oni had always felt he wanted to become friends with humans.

soko de, "{kokoro no yasashii} oni no uchi desu. donata demo oide-kudasai. {oishii} okashi ga gozaimasu. ocha mo wakashite-gozaimasu."
そこで、「心のやさしい鬼のうちです。どなたでもおいでください。おいしいお菓子がございます。お茶も沸かしてございます」
Given that, "Home of an oni {of gentle heart}. Anyone is welcome. [I] have {tasty} sweets. And [am] boiling tea."

touiu tatefuda wo kaki, ie no mae ni tatete-oita.
という立て札を書き、家の前に立てておいた。
Such signpost [he] wrote, and put [it] in front of [his] house.

shikashi, ningen-tachi wa utagai, dare hitori toshite aka-oni no ie ni asobi ni kuru koto wa nakatta.
しかし、人間たちは疑い、誰一人として赤鬼の家に遊びに来ることはなかった。
However, the humans doubted, not a single one came play at the red oni's house.

aka oni wa {hijou ni} kanashimi, {shin'you shite-moraenai} koto wo kuyashigari, {tsui ni} hara wo tate, {sekkaku tateta} tatefuda wo hiki-nuite-shimatta.
赤鬼は非常に悲しみ、信用してもらえないことを悔しがり、終いには腹を立て、せっかく立てた立て札を引き抜いてしまった。
The red oni was {extremely} saddened, frustrated for {not being trusted}, finally he lost [his] temper, and removed the signpost [that] {[he went through the effort of placing]}.

{hitori kanashimi ni kurete-ita} koro, tomodachi no ao-oni ga aka-oni no moto wo otozureru. {aka-oni no hanashi wo kiita} ao-oni wa {aru} koto wo kangaeta.
一人悲しみに暮れていた頃、友達の青鬼が赤鬼の元を訪れる。赤鬼の話を聞いた青鬼はあることを考えた。
By the time {[he] was overcome with lone sadness}, the friend blue oni came visit the red oni. {Having heard the red oni's story} the blue oni thought of {one} thing.

sore wa, "ao-oni ga ningen no mura e dekakete oo-abare wo suru. soko e aka-oni ga dete-kite, ao-oni wo korashimeru.
それは、「青鬼が人間の村へ出かけて大暴れをする。そこへ赤鬼が出てきて、青鬼をこらしめる。
That was [a plan]: "the blue oni departs to the human village and goes berserk. There the red oni shows up, and punishes the blue oni."

sou sureba ningen-tachi nimo {aka-oni ga {yasashii} oni da} toiu koto ga wakaru darou" touiu saku de atta.
そうすれば人間たちにも赤鬼がやさしい鬼だということがわかるだろう」という策であった。
Doing that the humans too will understand that {the red oni is a {gentle} oni}, [I think.]"

shikashi, {{kore de ao-oni ga moushi-wakenai} to omou} aka-oni datta ga, ao-oni ga {gouin ni} aka-oni wo tsure, {ningen-tachi ga sumu} mura e mukau no datta.
しかし、これでは青鬼に申し訳ないと思う赤鬼だったが、青鬼は強引に赤鬼を連れ、人間達が住む村へと向かうのだった。
However, {{with this [I'd be doing something] inexcusable to the blue oni} thought} the red oni, but the blue oni brought along the red oni {forcefully}, aiming for the village {the humans lived in}.

soshite {tsui ni} sakusen wa jikkou sareta. ao-oni ga mura no kodomo-tachi wo osoi, aka-oni ga kenmei ni fusegi-tasukeru.
そしてついに作戦は実行された。青鬼が村の子供達を襲い、赤鬼が懸命に防ぎ助ける。
And then {at last} the plan was realized. The blue oni attacked the village children, the red oni earnestly protected and rescued them.

sakusen wa seikou shi, okage de aka-oni wa ningen to nakayoku nari, murabito-tachi wa {aka-oni no ie ni asobi ni kuru} you ni natta.
作戦は成功し、おかげで赤鬼は人間と仲良くなり、村人達は赤鬼の家に遊びに来るようになった。
The plan succeeded, thanks to that the red oni became friends with the humans, the villagers [started] {coming play to the red oni's house}.

{ningen no tomodachi ga dekita} aka-oni wa mai-nichi mai-nichi asobi-tsuduke, juujitsu shita mai-nichi wo okuru.
人間の友達が出来た赤鬼は毎日毎日遊び続け、充実した毎日を送る。
{Having made human friends} the red oni kept playing every single day, living every day fully.

daga, aka-oni wa hitotsu {ki ni naru} koto ga atta. sore wa, {{shin'yuu de aru} ao-oni ga are kara ichido mo asobi ni konai} koto de atta.
だが、赤鬼には一つ気になることがあった。それは、親友である青鬼があれから一度も遊びに来ないことであった。
But, the red oni had one thing {[he] wondered about}. That was, {{[his best] friend}, the blue oni hadn't come play a single time ever since that}.

{ima murabito to nakayoku kurasete-iru} no wa ao-oni no okage de aru node, aka-oni wa kinkyou houkoku mo kanete {ao-oni no ie wo tazuneru} koto ni shita.
今村人と仲良く暮らせているのは青鬼のおかげであるので、赤鬼は近況報告もかねて青鬼の家を訪ねることにした。
[The reason he is] {now living being friends with the villagers} is thanks to the blue oni, so the red oni, also to report the current situation, decided to {visit the blue oni's home}.

shikashi, ao-oni no ie no to wa kataku shimatte-ori, to no waki ni harigami ga hatte-atta.
しかし、青鬼の家の戸は固く締まっており、戸の脇に貼り紙が貼ってあった。
However, the blue oni's house door was shut tightly, besides the door a paper was sticker.

sore wa "aka-oni-kun, ningen-tachi to nakayoku shite, tanoshikute kurashite-kudasai. moshi, boku ga, kono mama kimi to tsuki-atte-iru to, kimi mo {{warui} oni da} to omowareru kamoshiremasen. sore de, boku wa, tabi ni deru keredomo, itsu made mo kimi wo wasuremasen. sayounara, karada wo daiji ni shite-kudasai. boku wa doko made mo kimi no tomodachi desu"
それは「赤鬼くん、人間たちと仲良くして、楽しく暮らしてください。もし、ぼくが、このまま君と付き合っていると、君も悪い鬼だと思われるかもしれません。それで、ぼくは、旅に出るけれども、いつまでも君を忘れません。さようなら、体を大事にしてください。ぼくはどこまでも君の友達です」
That was "Red oni-kun, please become friends with humans, live having fun. If, I, kept your company like this, you too would be assumed {to be an {evil} oni}. That's why, I, will depart on a journey but, I'll never forget you. Good-bye, please take care of your health. I'm your friend no matter what happens."

touiu ao-oni kara no oki-tegami de atta.
という青鬼からの置手紙であった。
Such farewell letter left by the blue oni.

aka-oni wa damatte sore wo ni-do mo san-do mo yomi-age, namida wo nagashita.
赤鬼は黙ってそれを２度も３度も読み上げ、涙を流した。
The red stayed silent read it two, three times, and shed tears.