The Tainei-ji incident was a coup in September 1551 by Sue Takafusa (later known as Sue Harukata) against Ōuchi Yoshitaka, hegemon daimyō of western Japan, which ended in the latter's forced suicide in Tainei-ji, a temple in Nagato Province. The coup put an abrupt end to the prosperity of the Ōuchi clan, though they ruled western Japan in name for another six years under the figurehead Ōuchi Yoshinaga, who was not related to the Ōuchi by blood.

The downfall of the Ōuchi had far-reaching consequence beyond western Honshu. Since the courtiers in Yamaguchi were slaughtered, the imperial court in Kyoto became at the mercy of Miyoshi Nagayoshi. Warriors across Japan no longer ruled through the court but only used it to confer legitimacy. The once-peaceful Ōuchi territories in northern Kyushu descended into warfare among the Ōtomo, the Shimazu, and the Ryūzōji, who struggled to fill the void. The Ōtomo came to control much of these former Ōuchi domains in northern Kyushu, and their city of Funai flourished as a new centre of trade after the fall of Yamaguchi. At sea, foreign trade with China also suffered. The Ōuchi had been the official handlers of the Japan-China trade, but the Ming Chinese refused to acknowledge the usurpers and cut off all official trade between the two countries. Clandestine trade and piracy replaced the official trade of the Ōuchi, as the Ōtomo, the Sagara, and the Shimazu vied with each other to send ships to China. In the end, it was the Portuguese traders, with their near exclusive access to the Chinese market, who became the most successful intermediaries of the Japan–China trade for the rest of the 16th century.