The governors of Osaka, Fukuoka and Aichi have expressed interest. “Aichi Prefecture and Nagoya possess all the functions necessary to serve as a second capital. I’m the first in the nation to make a bid,” Aichi Governor Hideaki Omura said. Fukuoka Governor Seitaro Hattori added Friday: “We will aim for the designation as ‘all Fukuoka’ by working with municipalities and the local business community.”

For purely historical value, I gotta say Kyoto.

https://en.wikipedia.org/wiki/Kyoto

Kyoto is one of the oldest municipalities in Japan, having been chosen in 794 as the new seat of Japan’s imperial court by Emperor Kanmu. …The emperors of Japan ruled from Kyoto in the following eleven centuries until 1869…The capital was relocated from Kyoto to Tokyo after the Meiji Restoration.

searches

Aw yeah.

https://en.wikipedia.org/wiki/Capital_of_Japan

As of 2007, there is a movement to transfer the government functions of the capital from Tokyo while retaining Tokyo as the de facto capital, with the Gifu-Aichi region, the Mie-Kio region and other regions submitting bids for a de jure capital. Officially, the relocation is referred to as “capital functions relocation” instead of “capital relocation”, or as “relocation of the Diet and other organizations”.[19][20]

In 2023, the Government of Japan moved the Agency for Cultural Affairs to Kyoto. This was the first time that a central government office has been relocated outside Tokyo since Tokyo was designated as the capital.[21][22]