In the middle of the 19th century, the Tokugawa Shogunate is on its last leg. With foreign powers arriving to establish relations with Japan, the isolationist nation is under immense pressure from both external and internal forces. After the U.S. Navy forcibly opens Japan's borders, the Japanese must contend with the arrival of the mighty Diana—a 52-gun frigate flying the colors of the Russian Empire.

Japan has little resistance against such a vessel and must negotiate. Having recently concluded a treaty with the Americans, Toshiakira Kawaji is assigned to work out something similar with the Russians. But talks with the temperamental commander Yevfimy Vasilyevich Putyatin prove difficult. As the discussions drag on, disaster strikes: a massive earthquake hits Japan's coast, causing damage to Russians and Japanese alike—but perhaps the tragedy can be the catalyst in bringing the two nations together.

Bakumatsu no Spasibo is based on the true events of Yevfimy Putyatin's diplomatic mission to Japan and the signing of the Treaty of Shimoda in 1855.