真盛寺, Buddhist temple in Suginami-ku, Japan

Shinsei-ji is a Buddhist temple featuring traditional Japanese architecture in Suginami-ku. Its grounds contain multiple gardens with peonies, weeping cherry trees, moss areas, rock formations with waterfalls, and bamboo groves that together create distinct spaces for reflection.

Founded in 1631 by Shinkan Shōnin, a monk from Iga Province, in Yushima (now Bunkyō ward). It moved to Yanaka in 1683, to Nakano-go in Honjo (now Sumida ward) in 1688, and reached Umezato in 1922. From 1673 it served as the family temple of Mitsui Takatoshi, founder of the Echigoya drapery shop in Nihonbashi, hence its nickname Mitsui-dera.

Shinsei-ji belongs to the Tendai Shinsei school, founded by Shinsei Shonin, and serves as its Tokyo branch temple. It is the family temple of the Mitsui family, whose ancestor Takatoshi Mitsui founded the Echigoya drapery shop in Nihonbashi in 1673, so it is also called "Mitsui-dera". The temple grounds rank third in area among temples in Suginami Ward.

The temple is an eight-minute walk from Higashi-Koenji Station on the Tokyo Metro Marunouchi line. Buses on the Toei Shuku 91 and Shuku 66 routes stop at Sesion Suginami-mae, two minutes away, from Higashi-Koenji, Shinjuku and Asagaya stations. The grounds are not open to the public, so visits are limited to the exterior.

The grounds are thoughtfully divided into several separate garden areas, each with its own mix of plants and natural elements. This design choice allows visitors to experience multiple different natural scenes during a single visit.