Zojoji (増上寺) is a Jodo Buddhist temple located in the middle of Tokyo and is one of the largest Buddhist temples there. It was the tutelary temple of the Tokugawa Shogun family and thus used to possess fabulous mausoleums of the shoguns until they were burnt down in WWII. For details about this temple, see the article on Zojoji Temple.
The Gyoki-daie (御忌大会), held from April 2nd through 7th every year, is a series of rituals to commemorate the death of sect founder Honen (1133-1212).

Gyoki-daie

The Gyoki-daie is a ceremony held from April 2nd through 7th in memory of the death of sect founder Honen. Honen died on January 25 of 1212 so it used to be held in January but now it's held in April. Every day during this period, there will be chanting of sutras all day long by priests and worshippers. Other than this, there are some events outsiders can enjoy.

Bugaku

Every day from April 2 to 7, sometime around noon (it is announced to be held at "past noon" only, and when I went to see it, it started at around 0:30pm), there will be a bugaku dance performed in front of the main hall.

Nerigyoretsu

Nerigyoretsu is a procession held from April 5th through 7th from 1:30pm, starting from the Daimon and heading to the main hall of the temple. (The Daimon is the gate standing at around Daimon Station of the Toei Oedo Line or the Toei Asakusa Line.)

Nerigyoretsu is consisting of 200 to 300 participants clad in traditional outfits including priests and children.

When the parade reaches the main hall, priests conduct niwa-gishiki, which is a ritual praying for a successful sutra chanting which follows this event.

Kyozo

Kyozo is a sutra storage building built in the Edo period. Its inside is usually undisclosed, but during the Gyoki-daie, it will be open to the public and you can see the octagonal shelf for sutras in the building.