The shy girl or anime shy girl will refer to a commonly encountered type of character in manga/anime.
Characterized by cuteness to the point of adorability (or an eerie beauty, as in the case of Rei Ayanami), introversion, dark and/or blue hair, a fierce resolve to work harder, and a crush on the unaware male main character of the series. They could seem nerdish by wearing sweaters, glasses, or having their hair tied up or unkept, but would immediately become beautiful enough to be on the cover of a celebrity magazine by simply removing their glasses and adjusting their hair.
They sometimes involve an uncharacteristic encounter where the main character is shocked by a side of the character he hasn't seen before, often involving nudity, is a recurring theme as well.
Characters of this type so far listed are: