Ōken

The King's Key is the key of the royal house that can open a gateway to the dimension where the Spirit King is found. The only one in Soul Society that knows the location of the King's Key is the Commander-General (currently Shigekuni Yamamoto-Genryūsai). The location is passed on verbally from generation to generation, thus there is no document containing where it is located. The King's Key can be forged with 100,000 souls and a plot of spirit-enriched land with a radius of half a spirit-mile. The current spirit-enriched land in the real world is Karakura Town.