Iðunn

Iðunn (イズン) is a background mentioned in Shinyaku Toaru Majutsu no Index. He or she is a member of GREMLIN, 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 Gungir Arc
Sif 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 GREMLIN 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 GREMLIN and their invasion of Tokyo.