The Binzasara Dance is performed at the Sanja Matsuri to pray for a bountiful harvest. It is a form of dengaku — a type of performing art that developed from rice-planting ceremonies, which emerged in the Heian period and became widely popular from the Kamakura through the Muromachi era.
Performers dress in elaborate costumes and play the binzasara while beating a small drum, producing various sounds. They move through different formations, dancing to pray for a good harvest and to ward off evil spirits.
Binzasara Dance Today
On the first day of the Sanja Matsuri (Friday), the dance is performed as part of the grand procession through the streets of Asakusa. After arriving at Asakusa Shrine, the “Shinto Binzasara Dance” is dedicated at the haiden (worship hall) by parishioners, praying for a good harvest, prosperity in business, and the continuation of descendants. The dance is then also performed at the kagura-den (sacred stage).
What Is a Binzasara?
The word binzasara is written with characters meaning “bound wood” or “clapping boards.” It is an instrument made of several to around 100 thin pieces of bamboo or wood, bound together at the top with a cord, and is used in dengaku-style folk performing arts.
The binzasara used in the Shinto Binzasara Dance is made of 108 hinoki (Japanese cypress) wooden plates, each approximately 15 cm long and 0.6 cm thick. Held at both ends with both hands and opened and closed like an accordion, the plates strike each other to produce sound.
Source: Asakusa Shrine official page
https://asakusajinja.jp/sanjamatsuri/binzasara/