Tarnkappe

A Tarnkappe is a spiritual item based on a cloak of invisibility which appears in Norse Mythology.

Principles
Originally, it would have been a large cloak. The wearer’s strength would be enhanced and their body would be made invisible. somehow analyzed it and reconstructed its workings to turn it into a spiritual item in the form of narrow threads. The threads were laid out in the passageway of Brick Wharf and created a magical screen like the film of a soap bubble and the person’s form was erased from the background. It is capable of leaving virtually no trace to even Kanzaki's eyesight 8.0 eyesight that also has a certain level of night vision ability can see past. As she looked into the passageway to witch she could see no sign of the Alfar who was there, only upon focusing more trying to find her she noticed something like threads laid out through the darkened hallway.

Toaru Majutsu no Index SS: Kanzaki
During the events in Brick Wharf, Alfar initially hides herself, and an animal distorted by her power, from Kanzaki Kaori using a Tarnkappe made from silk threads.