Othinus

Age: Appears to be around 14 years
Classification: Magician
Affiliation:
GREMLIN (Leader)
Ability:
Magic God-related abilities, Odin-related abilities
Othinus is a Majin, which makes her a perfect and pure magician that encompasses every possibility. Because of this, since it is every possibility, she has an equal chance at succeeding and failing, making her magic a 50/50 shot. The reason she seeks to craft and wield Gungnir is to control the probabilities of her success and failure, effectively ridding herself of 50/50 restriction.

She is referred to as One-Eyed Othinus and, similarly to the Othinus of legend, she wears an eyepatch over her right eye which she has presumably lost in order for her to drink from the Well of Wisdom, though this may just be a ritualistic and aesthetic choice, as Othinus is maybe invoking Idol Theory to match that of Odin of Norse mythology. Her remaining eye is glittery green and with slit-like iris. She's seen dressed in a fur coat and a black leather outfit. She also wears a wide brimmed hat with a pointed tip, one which would have been worn by a witch.

(Source: Toaru Majutsu no Index Wikia)