Great works always seem to start at the hands of a single person and Kan'ei-ji is an example thereof. During the beginning of the Edo Era the Buddhist priest Nankobo Tenkai achieved the highest rank in priesthood of Daisojo. He had the trust of Tokugawa Ieyasu and became a liaison between the Imperial Court in Kyoto and the Tokugawa Shogunate set up in Edo, present day Tokyo. Tenkai was born in 1536 and died at the ripe age of 107 in 1643. During his long life he served also under the next two Shogun after the death of Ieyasu in 1616. Ieyasu had asked him in his last will to arrange his funeral and following two Shoguns, Tokugawa Hidetada and Iemitsu, asked him to built Kan'ei-ji. It was upon their wishes established northeast of Edo Castle for two reasons. The first one was protection for Edo Castle; a temple could easily be converted into a fortress if needed. Further, North-East was regarded as an unfavorable and unlucky direction in those days. The total area stretched from the area where Ueno Station now stands to the hills east and north of Shinobazu Pond. It housed more than 30 buildings and had enormous prestige and power because of the protection of the Shogunate it grew into the center of Buddhism in Japan. Its stature got raised even more when Shoguns began to choose the temple as their last resting place. Six of the 15 Shoguns were buried here.
Tenkai liked Lake Biwa very much and copied Shinobazu Pond and its island in the middle as an imitation of Chikubushima. Bentendo was then built on the island. The most important was however the Yakushirurikō Nyorai, the Master of Healing or Medicine Buddha. Unfortunately, in spite of all its might and wealth the temple was not spared for disasters. In 1657 the great Mireiki Fire destroyed a great number of buildings. A new hall was constructed in 1698. When the Tokugawa Shogunate collapsed during the Boshin War, the temple and surrounding buildings were destroyed during the Battle of Ueno under leadership of Saigo Takamori on 4 July 1868. The buildings were never restored. The main hall that can seen now was transferred from Kita-in, in Kawagoe in Saitama Prefecture, the temple where Nanboko Tenkei had once been a priest . It is not on the original site of Kan-eiji, but that of one of the sub-buildings. The bombardments during the Second World contributed highly to the further destruction. However the five-story pagoda, Bentendo and the Toshogu Shrine were among the most remarkable buildings and they have remained this way until today.