Dark Circles Under Eyes

In anime, sometimes a character has dark spots under their eyes, usually dark blue, or eye bags, baggy eyes, which are permanent and part of their design.

Character: Kuroki Tomoko 黒木智子
Anime: Watashi ga Motenai no wa Dou Kangaetemo Omaera ga Warui! 私がモテないのはどう考えてもお前らが悪い！ (Episode 1)

• In Japanese
• Meaning
• Examples
• References

3 Mouth

In anime, sometimes a character's "mouth becomes a 3," kuchi ga san ni naru 口が３になる.

Like this: ・3・.

Not like this: ・ω・. See nekoguchi 猫口 for mouths drawn like 3's rotated.

Character: Kuga Yuuma 空閑遊真
Anime: World Trigger, ワールドトリガー (Episode 2)

• Meaning
• Examples
• References

kuroshirome 黒白目

In Japanese, kuro-shirome 黒白目 means "black sclera"—the sclera being the (normally) white part of the eye.

Anime characters with black sclerae are often somehow inhuman. They may demons, cyborgs, androids, or other sort of robot, or have possibly demonic powers which, when activated, change the color of sclerae to black from white, maybe to imply the character has been corrupted.

Character: Genos ジェノス
Anime: One Punch Man, ワンパンマン (Episode 5)

• Meaning
• Examples
  
  • Transforming
  • Heterochromatic Sclerae
• References

shirome 白目

In Japanese, shirome 白目 means literally "white eye," and normally refers to the white part of the eye, the "sclera," kyoumaku 強膜, but can also refer to a character that has fully white eyes..

It's also spelled hakugan 白眼.

Character: Vega ベガ
Anime: Street Fighter II, ストリートファイターＩＩ (Movie)

• Meaning
  
  • Facial Expression
• Characters

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
• Examples
  
  • ASCII Art
• Origin
• References

nonojime 「の」の字目

In anime, sometimes eyes are drawn as the no の character, like this: の＿の. This means absolutely nothing. It's just a very simple way to draw eyes.

Character: Sakuragi Hinako 桜木ひな子
Anime: Hinako Note, ひなこのーと (Episode 1)

Above, the face of a "scarecrow," kakashi 案山子, drawn with the hiragana characters no の for eyes, mo も for nose, and he へ for mouth and eyebrows.

• Description
• Examples
• References

3 Eyes

In anime, sometimes characters' "eyes become 3's," me ga san ni naru 目が３になる. As in, they become drawn as the number 3, the Arabic numeral.

Not to be confused with having three eyes, or a cat mouth （・ω・）.

Character: Nobi Nobita 野比のび太
Anime: Doraemon ドラえもん (2005) (Episode 149, ねむりの天才のび太)

• Examples

gigan 義眼

In Japanese, gigan 義眼 means a "prosthetic eye," or an "artificial eye," as opposed to an innate one.

Character: Satomi Rentarou 里見蓮太郎
Anime: Black Bullet, ブラック・ブレット (Episode 4)

• Meaning
• Examples

magan 魔眼

In Japanese, magan 魔眼, "magic eye," or "demon eye," also called "evil eye," jagan 邪眼, or satirically jakigan 邪気眼, is an eye that has some sort of magical power or ability. Sometimes a cursed, evil, demonic one.

Character: Ryougi Shiki 両儀式
Anime: The Garden of Sinners: Overlooking View, Kara no Kyoukai: Fukan Fuukei 空の境界『俯瞰風景』 (Movie)

• Meaning
• Examples
  
  • Pair
  • Single
  • Extra
  • Fake
    
    • Imaginary

fukugan 複眼

In Japanese, fukugan 複眼, means "compound eyes," as in insect eyes.

Character: Beel Bub ベル゠ブブ
Anime: Shinchou Yuusha 慎重勇者 (Episode 8, Stitch)

• Meaning
• Examples
• References

Polycoria

Polycoria is the medical term for having multiple pupils in a single eye. It's commonly called "double pupils," or "pupula duplex," since it's normally only two pupils.

In Japanese, the common term for polycoria is choudou 重瞳, literally "stacked pupils," and the technical term is is ta-doukou-shou 多瞳孔症, "multiple pupil condition."

In anime, characters with natural double pupils are almost nonexistent. Honestly, I only know one example, and a pretty well-known one, too:

Character: Kaburagi Shisei 鏑木肆星
Anime: Shinsekai Yori 新世界より (Episode 18)

• Examples

tagan 多眼

In Japanese, tagan 多眼, "many eyes," refers to having three eyes or more.

Warning: if you have trypophobia, you probably don't want to read this article.

Character: Otoha 音翅
Anime: Sousei no Aquarion, 創聖のアクエリオン (Episode 1)

• Meaning
• Examples
  
  • Body
  • Face

Three Eyes

In anime, some characters have three eyes, with the third eye often being in the middle of the forehead, displaying some sort of special power.

Not to be confused with having 3 eyes.

Character: Pai パイ, Sanjiyan 三只眼
Anime: Sazan Aizu, ３×３ＥＹＥＳ (Episode 2)

• In Japanese
• Examples
  
  • Homogenous
  • Heterogenous
  • Vertical
  • Symbolic
  • Unusual

Cyclops Girl

In anime, a cyclops girl is an one-eyed monster girl, often with one impossibly large eye in the middle of her head.

The term for cyclops girl in Japanese is tangan-musume 単眼娘, "one-eyed girl," or tangan-shoujo 単眼少女, same meaning. They're also called "monoeye," monoai モノアイ, and hitotsume 一つ目, "one-eyed."

See the article about tangan 単眼 for details.

Character: Aiwarn アイワーン
Anime: Star☆Twinkle Precure, スター☆トゥインクルプリキュア (Episode 16)

• Examples

"One-Eyed" in Japanese

There are two ways to say "one-eyed" in Japanese:

1. sekigan
   隻眼
   For one-eyed characters that had two eyes, but lost one.
2. tangan
   単眼
   For one-eyed characters that always had one eye, cyclops-like.

Source: japanesewithanime.com (CC BY-SA 4.0)