This study examines the seas of Kyushu by distinguishing the north and south waters of Kyushu. First, it talks about the Goto Islands and Japanese missions to Tang China, especially with focus on the Fukue Island (福江島), which is the biggest of the Goto Islands and is located in the southeastern most part. Moreover, this study examines the Nansei Islands stretched out in a long arc in the southeast of Kyushu and the East China Sea (東支那海) surrounding these islands. It also explores the significance of interchange with the East Asian world including ancient Japan through the sea routes of the Goto Islands and Nansei Islands that are the north and south of Kyushu. As a result, we can analyze the East Asian world that had not been receiving much attention in the past from the outside in a new perspective. Furthermore, this study on the sea routes of the Goto Islands and Nansei Islands can extend the research accomplishments that had been focused on land. There was an imbalance in examining the members of the East Asian world with focus on land. In contrast, looking at this world from the sea implies that they could seek mutual exchange in equal positions.