Hosenji is a Shingon Buddhist temple which is a 5-min walk from Nakano-sakaue Station of the Tokyo Metro Marunouchi Line or the Toei Oedo Line. See the article on Hosenji Temple for details about this temple.
On Setsubun Day, which used to be the day before the spring begins but now fixed to February 3rd, many Shinto shrines and some Buddhist temples (most of them large ones) hold bean-throwing events (generally speaking, Shinto shrines call this festival the Setsubun-matsuri and Buddhist temples call this event the Setsubun-e, though there are exceptions). Hosenji, though not so large a temple, also holds the Setsubun-e, accompanied with a sohei (monk warrior) procession and a saito-goma (fire ritual.)
People clad in monk warrior costumes start parading from here [MAP] at 3:30pm. They first go south, then proceed along the main street, and head north at the south of the temple. (Monks in green clothes are ordinary monks.)
Monk warriors existed until the 16th century but disappeared when Toyotomi Hideyoshi, the war lord who reunified war-torn Japan in the latter half of the 16th century, disarmed Buddhist temples which possessed their own powerful armies.
At 4pm, a saito-goma, which is a kind of fire ritual, takes place. The head priest makes some gestures while chanting sutras.
After that, he sets fire on the branches.
While monks chant sutras and beat a drum, people throw gomagi in the fire. A gomagi is a piece of wood which you write down your wish on it, and it's sold in the precincts for 500 yen a piece.
Soon after the saito-goma ends, bean-throwing begins from 4:30pm.