Dvergr

Dvergr (黒小人(ドヴェルグ)) is a term used to refer to dimutive humanoid beings of Norse mythology. It is most popularly referred to as dwarf. In the Toaru Majutsu no Index universe, the magical nature of Dvergr is doubted, and are referred to as simply a different race of human beings instead of an altogther different group of beings.

Etymology
Dvergr is derived from the Old Norse name for the dwarf, though the true origina of the word is contested.

The kanji (黒小人) can be translated as Black Child, most likely referring to their dark skin, as exemplified by Marian Slingeneyer.

Appearance
Much of their appearance is as of yet unknown, although, one can presume due to their depictions in popular culture that they are swarthy and have statures shorter than that of an average human being.

Culture
Continuing with the doubts of their existence, Dvergr are apparently gifted in techniques in manufacturing metals that were unknown to Nordic cultures, and are apparently well suited to underground areas.

As of November 10th of the current timeline, Dvergrs have apparently become extremely rare.

Toaru Majutsu no Index SS: Norse Mythology

 * Main article: Toaru Majutsu no Index: Kanzaki SS

They are first mentioned during Kaori's investigation on Alfar, a girl who was designed to look like an elf of Norse legend. Here, Dvergrs or dwarves are referred to as apparently just a race who have metallurgy techniques unknown to the Nordic peoples. Alfar was also designed to apparently act like that of an elf, as having disdain for metal and the underground.

Hawaii Invasion Arc

 * Main article: Hawaii Invasion Arc

Marian Slingeneyer of GREMLIN, appears for the first time after the failed invasion Hawaii, talking to Othinus over the phone regarding their plans. Here, she refers to herself as a Dvergr, and shows craftmanship by showing Mjölnir type construct to Cendrillon, as her creation. She later threatens an injured Cendrillon that she would turn her into some mundane object of her choosing, and shows of her crafting tools.