Palace of Reflection: Kagami

History
Kagami along with the other Century Arms was forged in Lemuria through a taboo method. When the Collapse occurred, it and the other arms were scattered and lost across the planet, with Kagami coming to reside in Yamatai. It reactivated in the late Yayoi period, and connected with The shaman Queen Himiko. Upon Himiko's death the mirror went inert and was passed down through Himiko's successors. It was eventually shipped to the mainland as a act of peace between the emperor and the Queen, Kagami was retitled as Yata no Kagami and became one of Japan's three imperial regalia.

During the end of WWII, after the nuking of both Hiroshima and Nagasaki, a B-29 carrying the third atomic bomb "Loud Lady" went rouge. They planned to drop the nuke on Tsu, Mie, ignoring the Japanese surrender, which would have restarted the war. However, Kagami responded to one of the priestess at the Isu Grand Shrine, and was able to completely reflect bomb, destroying it and the rouge B-29 in a quick bright flash. This event notified the Japanese Sigea branch, and they were able to replace it with a fake mirror which had been infused with some of Amaterasu's divinity. Since then the mirror has been inactive and contained.