Family name Sousai (Sousai 
) , in the entire world, is a rare surname. The surname Sousai is habitual in Japan, where it is a rare surname, Brazil, where it is an extremely rare surname, and the United States. Not in comparison with a country's population, the name is most common in Japan, Brazil, and India. Much less frequently, Sousai is the forename as well as the last name.