This matsuri is probably one of the more bizarre Japanese festivals, when almost naked men (women can also participate, but wear a yukata) cleanse themselves with ice cold water while being cheered up.
The cleansing happens on Saturday in the morning (be there around 10am), whereas on Sunday you will see the hocho-shiki, which is a tradition in Japanese cuisine hailing from the Heian period and is a ceremonial slicing of a big carp fish by masters in the art.
Organizer and contact (Japanese): https://www.kandamyoujin.or.jp/
via Tokyo’s Festivals:
Tokyo’s Festivals presents an overview on Tokyo’s great festivals (mostly free festivals about food, culture, fireworks and music), so that more people find out about Tokyo’s best events. If you are interested in festivals in Tokyo, feel free to visit and like their page (Link: fb.com/TokyosFestivals) and follow their instagram (Link: instagram.com/tokyosfestivals).