Japanese imperialism was one of the most important driving forces in the history of modern East Asia. One influential group of actors at the grassroots level were the so-called ‘continental adventurers’ (tairiku rōnin) – Japanese nationals who travelled in Korea and China on the lookout for adventures and employment opportunities. Some of them worked part time for the army as spies, translators, and agents for special operations. These adventurers have been studied before as agents of Japanese imperialism, but existing accounts fail to present a convincing model of the mechanism that made their activities effective. The goal of this article is to fill this gap. This mechanism, which I shall hereafter call ‘the military-adventurous complex’, was a lobby of officers, continental adventurers, businessmen, politicians, criminal elements as well as Chinese, Manchurian, and Mongolian revolutionaries. The interests of these contingents were unique but nevertheless intertwining. Despite its decentralized character, the military-adventurous complex had a significant impact on Japanese foreign policy over an extended period. In this article, we shall explore the contours, structure, and modus operandi of that complex, its ambivalent relationship with the Japanese state, as well as several examples of its operations in the early twentieth century. Finally, we shall dwell on the ramifications of the complex on the development of Japanese imperialism.