Scrolls and paintings from the sixteenth century show them coming. Along the China coast, the seaborne gangs were marauders, murderers, kidnappers, and extortionists, terrorizing villages, stealing children and women. Accounts indicate that they arrived in swarms of boats as raiding parties numbering hundreds as they struck along coastal settlements, burning and pillaging. Storehouses were looted, farmers murdered, graves robbed. Victims were tortured, scalded, and disemboweled, sometimes for entertainment. Chinese troops serving provincial authorities were helplessly overmatched and fled; official residences were ransacked and burned, boats and ships confiscated.

The marauders, called kaizoku or wako, were societies unto themselves, often bound by loose feudal codes and chiefs, occupying coastal settlements beyond the reach of imperial or prefectural authority. Some established formidable outposts on small islands and ruled as local lords; many lived around inlets and mazes of sandbars under no political control. Originally Japanese from coastal provinces under the nominal authority of reckless daimyo, they preyed on Korean and Chinese merchants. Historically, they were in fact from no single country. Dominant Japanese clans would gradually be organized by Chinese raiders, with crew from across East and Southeast Asia.