Iðunn

Iðunn (イドゥン) is a background character mentioned in Shinyaku Toaru Majutsu no Index. They are a member of Gremlin (Norse), the powerful magic faction that shook the world in its foundations.

Etymology
Iðunn's name is based on a goddess from Norse mythology, who is associated with apples and youth, and according to the Prose Edda is the one who keeps the gods from growing old.

Lance of Gungnir
Iðunn is mentioned in passing, alongside Sif, by Marian Slingeneyer after Othinus becomes weakened after forcing the Holistic esper created from Kakine Teitoku's Dark Matter to continue its singing for the production of Gungnir. Here, Marian suggests to Othinus the two members, who currently have no duties, to handle her affairs for her for the production of the lance. Othinus however turns Marian's proposition down and goes off to mend herself.

It is unknown where Iðunn is during the course of the massive worldwide operation by and their invasion of Tokyo.

VS the World
Iðunn is mentioned in the conversation between Hel, Jörmungandr and Fenrir at Egeskov Castle with other members of, waiting for Othinus to arrive and take revenge for her abandonment of them, surprising the group, having been part of the rear guard alongside Sif. Iðunn is likely among the pile of scattered bodies when Touma and Othinus arrive at the castle.