Naha is the capital of Okinawa Prefecture, the tropical island group south of mainland Japan. The modern city was officially founded on May 20, 1921. Before that Naha had been for centuries one of the most important and populous sites in Okinawa. In the medieval and early modern periods, it was the commercial center of the Ryūkyū Kingdom.

Seoul, officially the Seoul Special City, is the capital and largest city of South Korea. A megacity with a population of over 10 million, it is one of the largest cities in the world. The Seoul National Capital Area is the world's second largest metropolitan area with over 24.5 million inhabitants, which includes the Incheon metropolis and most of Gyeonggi province. Almost half of South Korea's population live in the Seoul National Capital Area, and nearly a quarter in Seoul itself, making it the country's foremost economic, political, and cultural center.

Yokohama is the second largest city in Japan by population, and most populous municipality of Japan. It is the capital city of Kanagawa Prefecture. It lies on Tokyo Bay, south of Tokyo, in the Kantō region of the main island of Honshu. It is a major commercial hub of the Greater Tokyo Area. It’s also known for Sankei-en Garden, a botanical park containing preserved Japanese residences from different eras, and the seaside Minato Mirai district, site of the 296m Landmark Tower.   Yokohama's population of 3.7 million makes it Japan's largest city after the Special Wards of Tokyo. Yokohama developed rapidly as Japan's prominent port city following the end of Japan's relative isolation in the mid-19th century, and is today one of its major ports along with Kobe, Osaka, Nagoya, Hakata, Tokyo, and Chiba.