What are the three sacred treasures of Japan?

Japanese legend says that the Sun-goddess Amaterasu ruled over the Plain of High Heaven, and her Storm brother’s empire was the sea Plain. But Susanowo, her brother, was so violent that Amaterasu hid in a cave and plunged the world into darkness. She peeped out when the gods hung a necklace and mirror in a tree, and light returned. Susanowo was banished to the earth. He killed a monster, and found a sword in one of its eight tails. This he gave to his sister as a peace offering. So the Imperial Regalia of Japan consists of a sword, mirror and necklace.