What is the Japanese fighting dog breed, called "sumo inu" and created for dog sumo fights?

It was originally bred in Tosa (present day Kōchi) as a fighting dog, by crossing Shikoku-Ino crossed with European dog breeds, such as Mastiff, St. Bernard, Great Dane and the Bull Terrier. The heyday of Tosa breeding was between 1924 and 1933, today the breed is rare. Ownership of Tosas is legally restricted in many countries.