This article examines the process of diffusion of bird-pair antenna-style daggers and swords in southern Manchuria, the Korean peninsula, and northern Kyushu, analyzing the distribution of the daggers and swords, classifying them, and establishing a chronology. The daggers are classified into three types and sub-divided based on blade, handle, and pommel characteristics. Each form was produced and used at different time periods and in different areas, emerging first in the Jilin-Changchun region, then expanding into the Northern Liao region, Pyongyang, and as far as Tsushima and northern Kyushu. The bird-pair antenna-style dagger of Northeast Asia is unlikely to have been a trade item imported from outside of the region. It is more likely a local development as indigenous cultures that manufactured mandolin-shaped or slender bronze daggers were influenced by the bronze cultures of northern Asia and Ordos, the upper part of the Yellow River. This new type of dagger possibly represented a symbolic or prestige good reflecting political or economic alliances within the Puyŏ state of southern Manchuria or the early Wiman Chosŏn state in Pyongyang or among the statelets of Pyŏnhan and Chinhan in the Yŏngnam region. The bird-pair antenna-style daggers eventually flourished in the Yŏngnam region, where a local style developed. These daggers in turn diffused via immigration and trade to Tsushima in the mid-first century b.c.e.