Fraulein Kreutune

Kreutune is a mysterious, seemingly human, woman who has existed since the age of witch hunts.

She has the appearance of a woman who is almost two meters tall. She has silver hair, which is depicted as lavender in the illustrations instead of Index's "blue" silver hair. Moreover, the hair is unkempt and is long enough to reach her ankles and obscure her face. Her clothes consist of a two-piece transparent dress made out of synthetic fiber, revealing her pink underwear.

She is seen by Touma as having inhuman characteristics, despite no obvious signs of being different from a regular human being, just a feeling of something singularly off regarding her appearance, most likely similar to the Uncanny valley.

(Source: Toaru Majutsu no Index Wiki)