According to the Ministry of Defense, the vessels sailed between Okinawa's main island and Miyako Island on August 31st, heading toward the East China Sea. The two ships had previously passed through the Tsushima Strait on July 24th and the Soya Strait on August 8th, effectively completing a circuit of Japan via the Pacific Ocean.
When transiting the Soya Strait, the Chinese destroyer was accompanied by a Russian destroyer. The Ministry believes the two navies were engaged in a "joint patrol" in the Pacific.
Japan's Self-Defense Forces deployed patrol aircraft and other assets to conduct monitoring and intelligence gathering throughout the voyage.