The Sunpu Grand Imperial Palace period (1607-1616) lasted less than 10 years, but it was an extremely rich period in terms of its content. Specifically, it was a period of dynamic international diplomacy during which the royal envoys of the Netherlands, England, and Spain visited Sunpu.

At the time, the grand master Tokugawa Ieyasu dreamed of Sunpu Castle, which would have involved a major renovation of the Abe River, connecting Sunpu Castle with the castle grounds via a canal, and allowing ships from European countries to land directly beneath the castle tower. Unfortunately, the Abe River's currents sometimes became a "choppy river," making it impossible to realize this vision of a riverside castle and castle town, which led to the current location of Sunpu Castle Park.

The great lord Tokugawa Ieyasu played a leading role in Japan's Age of Exploration, centered on this Sunpu Castle, and developed a wide variety of diplomatic activities in Sunpu.

Even though the Grand Highness Tokugawa Ieyasu retired from the shogunate and moved to Sunpu Castle, he was not simply living in "retirement. Although Ieyasu Tokugawa was called the emperor by foreign envoys, not a single foreigner saw him as a "retiree". Rather, he kept a watchful eye on the Sunpu Castle, and, while holding more power than the second shogun, Hidetada, he kept the various feudal lords and court nobles under control.

The emissaries, missionaries, and merchants called Tokugawa Ieyasu of Sunpu "Emperor of Japan, Emperor of Japan, King of Japan, King of Japan, Daifu-sama, Grand Highness, Grand Emperor, Highness.

The king of Zipangu, the land of gold, that was what the great lord Tokugawa Ieyasu looked like in Sunpu.

It was during this period of the Sunpu Grand Imperial Palace that Japan began full-fledged international diplomacy, involving Europe and other parts of Asia. Sunpu became an important stage for international diplomacy, as many people from Europe, Southeast Asia, Southeast Asia and Korea came to Sunpu.

Dutch, English, and Spanish emissaries visited Sunpu one after another and concluded trade agreements. The words and deeds of Ieyasu Tokugawa, the Great Prince of Japan, had an impact not only domestically but also abroad. Ieyasu's international diplomacy extended not only to Europe and Southeast Asia, but also to Mexico across the Pacific Ocean.

For some reason, Ieyasu showed deep interest in trade with Mexico. He had William Adams (Anjin Miura) build a ship (a small 120-ton sailing ship) that successfully crossed the Pacific Ocean in 1610. This was the "Great Imperial Envoy to Mexico. This was the first time that a ship built by a Japanese national crossed the Pacific Ocean.

The Aoba venue of the Shizuoka Festival is themed around stories passed down through the generations in Shizuoka City, including the tale brought by Tokugawa Ieyasu, the champion of the Age of Discovery.