Over a span of 260 years, from 630 to 894, Japanese embassies to Tang China played a vital role in importing Tang governance and culture to Japan, significantly shaping the political and cultural landscape of an emerging Japanese state. The seventeenth embassy (836–839), fraught with turmoil, marked the final mission to Tang China. Alongside disasters and significant loss of life during the voyage, mysteries persist around Vice-ambassador Ono no Takamura's refusal to board ship, the government's insistence on the mission, and the objectives behind dispatching this mission to China. Drawing upon a rich tapestry of historical sources, including records from Shoku Nihon koki and the accompanying monk Ennin's Nit-To guho junrei koki, the author traces the journey from departure to return, focusing on the individuals involved and the prevailing trends of the era, offering a comprehensive examination of a transformative chapter in ancient Japanese diplomatic history.