The shrine was founded in 1627 when a senior monk of the Eitai-ji temple, Chōsei Hōin (長盛法印), received oracular guidance in several dreams to build a shrine at Eitaijima, the then name for the area where the shrine currently is. A variation on this says that Chōsei was a descendant of Sugawara Michizane and had in his possession an image of Hachiman made by the master. Chōsei was living in Kyōto when he had his dream and he was instructed to go to Edo and find an appropriate place to house the image. The year was 1624. He went to Edo and after wandering the streets for a long time found a hokora (small shrine) in what was then the largely unpopulated Eitaijima area. After three years of work reclaiming the wetlands with his own hands he was finally able to open the shrine in 1627.
Another account tells us that this Tomioka Hachiman-Gū is a branch of the one in Kanazawa-ku in Yokohama. In the early Edo Period land reclamation was underway in the area and as a result of this work running into difficulties the shrine was spun off from the one in Kanazawa-ku through the bunrei process and was apparently temporarily known as Namiyoke (Seawall) Hachiman. The amount of land reclaimed and then owned by the shrine was slightly over 200,000 m2. The Tokugawa Shōgunate supported the shrine; along with the Meiji Restoration it was given Junchokusai status and in 1975 it became one of the Ten Tōkyō Shrines.
(Note: numbers in parentheses after kami names
From Merged Shrines
Takenouchi no Sukune 武内宿禰
Ame no Koyane no Mikoto 天兒屋命
Kashima Jinja 鹿島神社
Eishōgosha Inari Jinja 永昌五社稲荷神社
Tenman Ten Jinja 天満天神社
Nominosukune Jinja 野見宿禰神社
Nanawatari Jinja 七渡神社
Annual Festival: August 15
Since 1999 the shrine has been rocked by a series of scandals, including conjugal killing and financial skullduggery, and in 2013 family squabbling resulted in withdrawal from the Association of Shinto Shrines. The Japan Times has a detailed story here.
Tomioka Hachiman-Gū was the birthplace of modern professional Sumo. Perhaps unsurprisingly the sport developed in the Kyōto/Nara/ Ōsaka region, but there were many problems surrounding it and it was banned from time to time. In 1684 the Bakufu lifted the ban then in place and allowed Spring and Autumn tournaments. They were held in Tomioka Hachiman-Gū, and they continued to be held there until 1781, when they were moved to the Ekōin-ji (回向院) temple in Ryōgoku.
Three minutes' walk from Monzen-naka-chō Station and set amidst the 16,700m2 Fukagawa Park, one of Tōkyō's oldest. There is much to see in the shrine; for most visitors the most interesting sights are probably the two clumps of Sumo-related monuments. One of the most picturesque aspects of the shrine is the Nanawatari Jinja and the lake it nestles in. Well worth a visit.
The shrine was destroyed by fire in 1683, by earthquakes in 1703 and 1923, and finally by the firebombing of March 10, 1945. Rebuilding of the main hall, a ferro-concrete structure, was completed in 1956.