Fire Festival

The Fire Festival is an annual event in Wano Country.

Overview
The Fire Festival is an annual celebration, held by the residents of Wano Country's capital, the Flower Capital to commemorate the Beasts Pirates saving the nation from the "evil" Kozuki Family. During the event, the Shogun of Wano, Kurozumi Orochi, and his procession travel to Onigashima, Kaido's residence, to show to country gratitude.

However, this is a facade as the real purpose is for the Shogun to have a banquet with his allies at the expense of the residents.

Past
20 years ago, as part of the Beasts Pirates and the Shogun of Wano, Kurozumi Orochi, plot to take over Wano Country from the Kozuki Family, Orochi had the head of the family, Oden executed, while the beast pirates burn down the family's home, the Oden Castle, seemingly killing the rest of the family and their allies. Following that, the Shogun and the pirates took control on the land, and claimed to have free to country from Oden's dangerous "Open Country Idea".

Believing the Beast pirates has issued in an era of peace, the residents of Wano started celebrating their feat, and established the festival as a way to pay their respects to the crew.

Wano Country Arc
About two weeks before the upcoming festival, Monkey D. Luffy has arrived to Wano, as for the Ninja-Pirate-Mink-Samurai Alliance's plan to take down Kaido. Shortly after his arrival, he met with Kin'emon that explained the alliance plan of attacking the Beast Pirates on the night of the festival.

A week later, the shogun of Wano, Kurozumi Orochi, had a private prelude party for his close allies. For her part in the alliance's plan, Nico Robin infiltrated the party under the guise of one of the dancing geisha in order to get close to the shogun.

Trivia

 * Traditionally, a real world fire festival is a common Japanese custom of igniting a large bonfire during celebratory events.