Invisible Air: Bounded Field of the Wind King (風王結界インビジブル・エア, Fū-ō KekkaiInbijiburu Ea?) is a sheath of wind that covers Excalibur and conceals it so that it cannot be easily recognized as the famous holy sword of King Arthur and expose her identity. It is a Bounded Field closer to magecraft than a Noble Phantasm that is made up of multiple layers of wind compressed into super-high pressure air with a massive amount of magical energy, which distorts the refraction of light and renders what is inside completely invisible. For the male King Arthur, Invisible Air acts as one of the seals along with the Restraints of the Round Table to Excalibur Proto's true power. While it has no basis in history, Kinoko Nasu figures it would be something Merlin could have managed because Heroic Spirits with