Time Out says
An Edo-era legend holds that paying one's respects at a temple dedicated to the bodhisattva Kannon on shimanrokusen-nichi (July 10) will count for the same as 46,000 such visits on any other day. Such convenience obviously appealed to Edoites, who never passed on the opportunity to receive a few extra blessings. The Hozuki-Ichi, named after the flower that resembles a red paper lantern and was once believed to have healing properties, takes place over this lucky pair of days and will see up to 100 flower stalls set up around Sensoji Temple. Special charms are also sold at the temple during the festival, so remember to check out the selection.