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

Meaning

The word gigan 義眼 is the normal Japanese word for prosthetic eyes. It's composed by morphemes:

• gi
  義
  Not innate. Prosthetic. Artificial.
• gan
  眼
  Eye.

To have a better idea, some related words:

• gisoku
  義足
  Artificial leg.
• gishu
  義手
  Artificial hand.
• giri no imouto
  義理の妹
  A younger sister not related by blood.

Examples

In anime, when characters who have lost one eye, who are "missing one eye," sekigan 隻眼, get a prosthetic eye, the prosthetic eye tends not to be just a simple prosthetic eye. That is, the artificial tends to have superpowers.

For example, they tend to be cybernetic eyes capable of seeings things very far or very small, of seeing in the dark, of doing calculations, all that sort of sci-fi stuff. When they such powers, they also count as magan 魔眼, "magic eyes," even if they aren't magical.

Character: Leonardo Watch レオナルド・ウォッチ
Anime: Blood Blockade Battlefront, Kekkai Sensen 血界戦線 (Episode 2)

• kamigami no gigan
  神々の義眼
  Prosthetic eyes of the gods. Artificial eyes of the gods. Known in English as the All-Seeing Eyes of the Gods.
• Allows the bearer to see through illusions. Can see extremely small things. Can project what they see into other people's sight. Can do a whole lot of things, to be honest.

Since the prosthetic eye is an acquired eye, it's possible for it to have a different color from the natural eye, giving the character different-colored eyes.

Character: Asama Tomo 浅間智
Anime: Kyoukaisenjou no Horizon, 境界線上のホライゾン (Episode 1)

And then there's this:

Character: Daniel Dickens ダニエル・ディケンズ
Anime: Angels of Death, Satsuriku no Tenshi 殺戮の天使 (Episode 1)

• Heterochromatic double-pupils artificial eyes. Because why not.