Surname Koseko (Koseko 
) , throughout the world, is a rare family name. The cognomen Koseko is characteristic of Japan, where it is a rare surname, Brazil, where it is a very rare surname, and Malaysia, where it is an extremely rare surname. Not in comparison with a country's population, it most frequently occurs in Japan, Brazil, and Nigeria. Much less frequently, Koseko is the forename as well as the last name.