Sakai is a city located in Osaka Prefecture, Japan. It has been one of the largest and most important seaports of Japan since the medieval era. Sakai is known for its kofun, keyhole-shaped burial mounds dating from the fifth century. The kofun in Sakai include the largest grave in the world by area, Daisen Kofun. Once known for swords, Sakai is now famous for the quality of its cutlery. As of 1 January 2022, the city had an estimated population of 819,965, making it the fourteenth most populous city in Japan.

Kawachi Province was a province of Japan in the eastern part of modern Osaka Prefecture. It originally held the southwestern area that was split off into Izumi Province. It was also known as Kashū (河州).