Buzen is a city located in Fukuoka Prefecture, Japan. As of 31 December 2023, the city had an estimated population of 23,844 in 11794 households, and a population density of 210 persons per km². The total area of the city is 111.10 km2 (42.90 sq mi).

Nakatsu is a city on the northern border of Ōita Prefecture in Kyushu, Japan. As of 31 October 2023, the city had an estimated population of 82,301 in 41222 households, and a population density of 96 persons per km2. The total area of the city is 491.53 km2 (189.78 sq mi).