Aikido is the second opening of Ame no Iwato [the rock door of heaven].
Susa no Wo no Mikoto had been given the mission of developing
materialism and purifying the karma created in that process, but he
refused and was banished from Taka Ama Hara, the heavenly world. Upset,
he started a quarrel with his sister Amaterasu and later skinned a horse
alive and threw the bloody hide among the women who were weaving kimono
in Amaterasu's house. At this, Amaterasu became distraught and hid
herself in a cave behind a rock door. This caused the sun to disappear
from Taka Ama Hara and Ashi Hara (the earthly world) a well. The world
entered into eternal night, and the evil gods took advantage of this
situation by throwing the world into chaos. In order to remedy this
tragic situation, the gods had a meeting and decided to stage a huge
celebration. They asked the goddess Ame no Uzume no Mikoto to perform
an erotic dance. This made all the gods laugh and shout with great joy.
Inside the cave, Amaterasu, hearing the commotion, wondered how there
could be happiness in the world without her light and went to the door
to ask what was going on. Told that there was another deity much
greater than her, in jealousy she peeked out to see --- only to be
dazzled by her own reflection in a mirror that had been placed at the
door. At that moment she was caught by Ame no Tajikara Wo no Kami, a
god of great strength, who pulled her back into the world.
W. Gleason, The Spiritual Foundations of Aikido