Bon Odori

History (from Wikipedia)
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Obon (お盆, Obon?) or just Bon (盆, Bon?) is a Japanese Buddhist custom to honor the departed (deceased) spirits of one's ancestors. This Buddhist custom has evolved into a family reunion holiday during which people return to ancestral family places and visit and clean their ancestors' graves. It has existed in Japan for more than 500 years and traditionally includes a dance, known as Bon-Odori.
Bon Odori originates from the story of Mokuren, a disciple of the Buddha, who used his supernatural powers to look upon his deceased mother. He discovered she had fallen into the Realm of Hungry Ghosts and was suffering.[3] Greatly disturbed, he went to the Buddha and asked how he could release his mother from this realm. Buddha instructed him to make offerings to the many priests who had just completed their summer retreat, on the fifteenth day of the seventh month. The disciple did this and, thus, saw his mother's release. He also began to see the true nature of her past unselfishness and the many sacrifices that she had made for him. The disciple, happy because of his mother's release and grateful for his mother's kindness, danced with joy. From this dance of joy comes Bon Odori or "Bon Dance", a time in which ancestors and their sacrifices are remembered and appreciated.