Tanabata “Star Celebration”

Amaterasu Ōmikami holding Susanō’s sword along with the mirror, Yata no Kagami, and the jewel, Yasakani no Magatama. The sacred sword, mirror, and jewel collectively became the three Imperial Regalia of Japan.

Otherwise called the Star Celebration, Japan's Tanabata, (Hoshi Matsuri), has its foundations in the Chinese Qixi, "Double Seventh Festival". In contrast to the lunar calendar, it is typically observed on July 7, which is the seventh day of the seventh month in the Gregorian calendar in Japan.

Amaterasu Ōmikami, is the goddess of the sun in Japanese mythology. One of the major deities (kami) of Shinto. She wears a crown symbolic of the rising sun and is known as a kind Goddess who brings light, joy, and prosperity to her people. She is the daughter of the divine creators of the world, Izanami and Izanagi, and she has two brothers: Tsukuyomi, the God of the Moon, and Susanoo, the God of Storms and seas. The emperors of Japan are believed to be direct descendants of Amaterasu.

Amaterasu and her younger brother Susanō were always at odds. Susanō is a multifaceted deity with contradictory characteristics (both good and bad), being portrayed in various stories as a wild, impetuous god associated with the sea and storms.

Amaterasu had a mistrust of her brother younger brother so Susanō proposed a trial by pledge (ukehi) to prove his sincerity to her and she accepted. In the ritual, the two gods each chewed and spat out an object carried by the other.

Amaterasu broke Susanō's ten-span sword (totsuka no tsurugi) into three, chewed them and then spat them out. Three goddesses – Tagorihime, Ichikishimahime, and Tagitsuhime – were thus born.

Susanō then took the strings of magatama beads Amaterasu entwined in her hair and round her wrists, likewise chewed the beads and spat them out. Five male deities – Ame-no-Oshihomimi, Ame-no-Hohi, Amatsuhikone, Ikutsuhikone, and Kumano-no-Kusubi – then came into existence.

Amaterasu declares that the male deities were hers because they were born of her necklace, and that the three goddesses were Susanō's. Susanō, announcing that he had won the trial, thus signifying the purity of his intentions, "raged with victory" and proceeded to wreak havoc by destroying his sister's rice fields, defecating in her palace and flaying the 'heavenly piebald horse' (ame-no-fuchikoma), which he then hurled at Amaterasu's loom, killing one of her weaving maidens. A furious Amaterasu in response hid inside the Ama-no-Iwato ("Heavenly Rock Cave"), plunging heaven and earth into total darkness. The gods, led by Omoikane-no-Kami (思金神), eventually persuade her to come out of the cave, restoring light to the world. As punishment for his misdeeds, Susanoo is thrown out of Takamagahara (High Plane of Heaven).

Sources : Wikipedia (1) Amaterasu (2) Susanō no Mikoto