This structure contained the massive power supply and other equipment required to operate longwave radio transmission for the Imperial Japanese Navy. There were numerous fortified rooms under this building and dug into the surrounding landscape.

Lisa is taking a photo of one of the several tiny bats that were hanging out inside during the day.

WWII Allies had cracked all IJN codes towards the end of the war, so I'd speculate this facility was left unscathed when Allied aircraft were within range of mainland Japan in 1945 because, unbeknown to the IJN, its transmissions were an invaluable source of strategic and tactical information for the Allies.