osoroshii ko 恐ろしい子

In Japanese, osoroshii ko 恐ろしい子 means "what a terrifying child," or "what a terrifying girl," "what a terrifying guy," "what a terrifying person," and so on.

In manga and anime, osoroshii ko refers to a pose of shock, with eyes drawn completely white, and usually with one's index finger placed across the chin, sometimes drawn in monotone like manga, accompanied by background effects like thunder or flash lines, used when a character has realized the terrifying capability of somebody.

It originates in the drama shoujo manga, Glass Mask, Garasu no Kamen ガラスの仮面. Today, it's pretty much always used in comedy, often sarcastically. It's become a meme.

Rimuru Tempest リムル＝テンペスト
Anime: Tensei shitara Slime Datta Ken, 転生したらスライムだった件 (Episode 21)

Meaning

Literally, osoroshii 恐ろしい means "terrifying," or "horrifying." That which should be feared. While ko 子, meaning literally "child," can also refer to a person in general.

Due to ko 子 being used more by women than by men to refer to non-children, the phrase osoroshii ko is also used in anime more by girls than by guys.

Examples

For reference, some examples.

Rimuru Tempest リムル＝テンペスト
Anime: Tensei shitara Slime Datta Ken, 転生したらスライムだった件 (Episode 21)

Context: Rimuru Tempest リムル＝テンペスト, after one young child, Chloe Aubert クロエ・オベール, uses a dangerous spell against him and tells him that he's going to die if he doesn't admit defeat.
osanai kuse ni osoroshii ko!
幼いくせに恐ろしい子！
Despite being young, [she] is a terrifying child!

Mile マイル, Adele von Ascham アデル・フォン・アスカム, example of osoroshii ko 恐ろしい子.

Character: Mile マイル
Anime: Watashi, Nouryoku wa Heikinchi de tte Itta yo ne! 私、能力は平均値でって言ったよね！ (Episode 7)

Context: Pauline, a child of merchant, never forgets anything related to money, and has memorized every expense and earned income she's had ever since she graduated school.
{okane ni kansuru} koto wa wasuremasen yo
お金に関することは忘れませんよ
Things [that] {concern money} [I] don't forget.
I don't forget anything related to money.
Upon hearing that, Mile says:
shounin no chi!
Poorin-san, osoroshii ko!
商人の血！
ポーリンさん、おそろしい子！
The blood of a merchant!
Pauline-san, what a terrifying [girl]!

Raim ライム, example of osoroshii ko 恐ろしい子.

Character: Raim ライム
Anime: Mairimashita! Iruma-kun 魔入りました！入間くん (Episode 8)

Context: Raim ライム, a succubus, teaches a course of seduction in Babyls, the demon school of the demon world. She uses her special ability to measure the ~~power level~~ seductiveness of each student, which is shown in percentages.
42%, 63%, 51%. She says the lowest she has ever seen is 21%.
Then she measures Clara クララ, a goofy demon girl and one of the main characters.
ni... nipa... ni paasento?!
に・・・にぱ・・・２％？！
T... tw... two percent?!
akanbou demo san paasento wa eroi noni
{akanbou yori muku da} to iu no?!
赤ん坊でも３％はエロいのに
赤ん坊より無垢だというの？！
Even babies are [at least] three percent sexy,
[you're] telling [me] that [she's] {more innocent than a baby}?!
oo mai debiru!
オーマイデビル！
Oh my devil!

Amano Keita 天野景太, example of osoroshii ko 恐ろしい子.

Character: Amano Keita 天野景太
Anime: Youkai Watch, 妖怪ウォッチ (Episode 2)

Context: a youkai 妖怪 makes people spill secrets around without thinking, including, for example, the fact that Amano Keita 天野景太 went to toilet to poop.
{toire no dai ni haitta} koto made barashichau nante,
nante osoroshii youkai nanoda...
トイレの大に入ったことまでバラしちゃうなんて、
なんて恐ろしい妖怪なのだ･･･！
To even tell everyone [that] {[I] went to the toilet to poop},
what a terrifying youkai...!
- barashichau
  バラしちゃう
  (contraction of...)
- barashite-shimau
  バラしてしまう
  To barasu, with barasu being an unwanted outcome.
- barasu
  バラす
  To tell everyone a secret. (lexical causative of bareru バレる, for a secret "to be found out.")
- In Japanese, dai 大, "large," and shou 小, "small," may refer to daiben 大便, "feces," and shouben 小便, "urine." In English, the phrases "number 2" and "number 1" are used similarly.

Yellow: Juushimatsu 十四松
Green: Choromatsu チョロ松
Blue: Karamatsu カラ松
Pink: Osomatsu おそ松
Gray: Ichimatsu 一松
Anime: Osomatsu-san おそ松さん (Episode 7)

Context: the reaction of the older sixtuplets, when the youngest, Matsuno Todomatsu 松野トド松, tells them:
shouji ni iu yo
正直に言うよ
[I] will speak honestly.
boku wa, niichan-tachi no sonzai ga hazukashii
僕は、兄ちゃんたちの存在が恥ずかしい
I'm ashamed of [your], [my] older brothers', existence.
- See also: double subject construction.

Ristarte リスタルテ, example of osoroshii ko 恐ろしい子.

Character: Ristarte リスタルテ
Anime: Shinchou Yuusha 慎重勇者 (Episode 5)

Context: the reaction of the Goddess Ristarte when she realizes Mash マッシュ has been badly influenced by the cautious paranoia of Seiya 聖哉.
- Seiya tests Mash by asking how many torches they should buy to investigate the caverns, Mash answers "50," Seiya says the correct answer is "500," while Ristarte stops them to buy just "5" torches.
kono ko... Seiya ni doku sarete dougu kankaku ga okashiku natteru!
この子･･･聖哉に毒されて道具感覚がおかしくなってる！
This kid... [he] has been corrupted by Seiya and [now his common sense about] items [has become weird]!

An example of the phrase used without the image:

Izumi Konata 泉こなた, example of osoroshii ko 恐ろしい子.

Anime: Lucky☆Star, らき☆すた (Episode 7)

Context: Izumi Konata 泉こなた draws Hiiragi Kagami 柊かがみ on a piece of paper. Her sketch is awfully bad and shows her spitting fire. As Kagami starts getting angry, and is drawn in the anime spitting fire, Konata, in a rose-filled background, says:
maa..., Kagami-san tte {imeeji-doori no} okata desu yo ne... osoroshii ko!
まぁ･･･、かがみさんってイメージ通りの御方ですよね･･･恐ろしい子！
[My], Kagami-san was {just as [we] imagined [she were]}, [wasn't she]... what a terrifying child!
- tte って - topic marker.

And an example of the image being used without anything else:

Akino Sakura 秋野桜, example of osoroshii ko 恐ろしい子.

Context: Akino Sakura 秋野桜,
Anime: Ore wo Suki nano wa Omae dake kayo 俺を好きなのはお前だけかよ (Episode 2)

Context: Akino Sakura 秋野桜 is shook because something unexpected happened, but that's it. Nobody was an osoroshii ko in this scene.

ASCII Art

As ASCII art (author unknown), posted on text boards:

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　　　　　　　　｀　　 y__　　　　　 ''　　　'-　　||||! {-/ ／|　　　　 　 |
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　　　　　　　　〃 　　"'ｰﾉ　　　　　　　　 i　　||　 l/　　 |　 l　 　 　 |
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　　　　　　　　　　　／　 ／＼　｀ﾆ｀　　　　／ 　 l /　 | 　 ‐┼‐　　　ヽ
　彡三＝''　　 _,.-'"　／ 　 ／ ＼　　　 ／　　　/ /　 | 　 　 '　　　　　　＼

ヽ、__ ／　　　　　　　　　｀ヽ／　　｀ヽ　　＼
｀ｰ,.　　　/　　/　　　　　　ヾ〃ヽ　　　ヽ　　〉　　＼＼　|
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　　　　i/　/ / （(_j }　　/ ,.-‐‐‐‐,'/i　i　|　}　ヽヽ
　　 　 {　 {　ゝ､_,.ノ　　l|　｀‐--‐'､i/ ﾉ ﾉ　ﾉ　ノ　ﾉ　　 |
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　　　　ヽ _____ノ |　　　　　　　　 l'　/　　/　　{　　　　　・ ・

Origin

The origin of osoroshii ko is the manga "Glass Mask," Garasu no Kamen ガラスの仮面.

In the first chapter, a veteran actress, Tsukikage Chigusa 月影千草, finds a 13 year old girl, the protagonist, Kitajima Maya 北島マヤ, who appears to have talent for acting.

Maya works in a restaurant and goes deliver food to Chigusa. There, Maya mentions having watched a theater play, and Chigusa asks her to tell how that play went.

Maya then starts acting out, albeit poorly, the entire script of the play for over three hours, without mistaking a single line, and even showing to have memorized the poses and hand movements of the actors.

After Maya leaves, Chigusa, amazed by Maya's potential, exclaims:

Manga: Glass Mask, Garasu no Gamen ガラスの仮面 (Chapter 1, 千の仮面をもつ少女)

osoroshii ko!
恐ろしい子！
What a terrifying child!

As you can see above, in the first time the phrase was used, there was no panel that matched the meme this article is about.

In fact, Glass Mask didn't use the iconic fully-white, iris-less, pupil-less eyes until thousands of pages later.

It started using them as an extremely tense expression, like when a character has just heard some extremely bad news, and, also, as an extremely hostile expression, when a character is acting a ferocious role.

A collage of faces like osoroshii ko 恐ろしい子.

Manga: Glass Mask, Garasu no Gamen ガラスの仮面 (Various Chapters)

shirome
白目
White eye. (literally.)
Sclera. The white part of the eye.

Also, contrary to what you'd expect, the phrase osoroshii ko wasn't repeated through the series. Even the iconic panel, with white eyes and an index finger horizontally across the chin, didn't use the phrase osoroshii ko, but something else instead.

The origin of the iconic osoroshii ko 恐ろしい子 pose.

Manga: Glass Mask, Garasu no Gamen ガラスの仮面 (Chapter 12, 紅天女)

kono ko...!
この子･･･！
This child.
This [girl].

The character who spoke that line and made that pose was the main character's rival, Himekawa Ayumi 姫川亜弓, who was an ojousama お嬢様 character.

For the record, although the pose happened in chapter 12, each chapter of this series has hundreds of pages, and spans multiple volumes. The manga began in 1974, while the 12th chapter began serialization in 1986, ending in 1992.^{[美内すずえ(Suzue Miuchi) - comich.net, accessed 2020-02-20]}

It was basically the penultimate chapter of the manga, before it restarted in 2004, so the meme takes a phrase from the first chapter, and a pose from the almost last chapter, and puts them together.

References

恐ろしい子 - dic.pixiv.net, accessed 2020-02-20.
恐ろしい子 - dic.nicovideo.jp, accessed 2020-02-20.
恐ろしい子！/ ○○…恐ろしい子！ - paradisearmy.com, accessed 2020-02-20.