During Sailor Moon Super, the three awakened outer senshi are looking for three talismans: a mirror, a sword and a jewel. In Japanese culture, the mirror represents Truth and is one of the Three Treasures. The sword represents Courage and Strength, while the jewel stands for Compassion. All of these three treasures can be found in the Amaterasu myth.

Susano-O (known as Susa) went to visit his sister. He was about to make the journey to the underworld to be with their dead mother, and he was afraid of making the trip. To strengthen himself, Susa decided to spend a season with his sister’s light and wisdom. In his haste to see Ama, Susa moved through the sky with a crackling thunder, shaking mountains and rivers and sending all living beings into hiding.

Even Ama became frightened. "Why do you disturb the peace of our kingdom, Susa?"
This was not what he was hoping to find. Susa replied in his most courtly manner: "O, radiant sister, I wish you no harm. My only desire is your warm company, a glimpse of your lovely face, and a few pleasant words before I descend to the underworld to find our most esteemed mother."

His answer pleased her, but Ama knew her brother well and decided to ask for proof of his good intentions. Susa then proposed that they should create children who would rule the blessed land wisely. Ama agreed. She took her brother’s sword, broke it into three pieces and after chewing the pieces for many days and nights, blew a light mist from her mouth, which gave birth to three beautiful goddesses.
Susano-O then asked his sister for the five jewels she was wearing, and after cracking them between his teeth, blew a light mist from his mouth and gave birth to five powerful masculine deities. Unfortunately, Susa began jumping around boasting of his omnipotence. Ama reminded him that the gods had been created from her jewels and Susa became enraged, losing all self-control. He released the wind and rain he held under his waving arms!

Ama forgave him, but his pity made Susa try to make her lose her temper. Susa flayed a piebald horse, made a hole in the roof of the house, and threw the dead horse into Ama's sacred chamber where she was weaving the god’s clothes. Ama, worn out, could only think of running away. She ran as far as she could to a rocky cave in a quiet corner of Heaven and she blocked the entrance with a boulder.

The world was left in darkness. Susa, in disgrace began the long journey to the underworld alone.
Amaterasu sat a very long time in the cave. People sat in their homes, listless and hopeless. The world began to wither and die.

Eight hundred myriad of gods gathered together to decide how to get Amaterasu back. They begged the god Hoard-thoughts to help them. He advised the gods to collect cocks. Next, he told the gods to hang a mirror with strands of jewels on the branches of a Sakaki tree, just at the entrance of Amaterasu’s cave.
Next, a sister-goddess, Ama no Uzume, stepped forward with an idea all her own. She began to dance. All the eight hundred myriad of gods roared with laughter and approval, hooting and hollering. By the light of a thousand torches, the cocks began crowing loudly in unison.
Amaterasu, in her cave, was surprised. Finally, when she heard the laughter of the gods, she couldn’t resist peering outside the cave.

Catching a glimpse of something in the mirror hanging in front of her, just for a moment Ama forgot her fear and pain and stood transfixed by a clear light. Amaterasu was seeing herself for the first time in a very long time, and it gave her a stronger determination to carry on her duties in heaven. She immediately returned to her palace and vowed never again to be so frightened by any storm. Mirrors were hung in the doorways to her temples, so that all who passed in or out might look deeply into it.

Taken from Lyricalworks