China and Japan face a tense situation in the East China Sea over conflicting sovereignty claims to the Senkaku Islands. In order to cope with the situation appropriately and precisely, Japan needs to thoroughly analyze it from the dual perspectives of the law of the sea and the law of territorial acquisition. Japan denies any existence of a dispute with China over the territorial sovereignty of the islands. The legal effects of the existence of a “dispute” need to be understood and considered by Japan when it constructs its position from the perspectives of the law of the sea and the law of territorial acquisition. This article analyzes those effects and proposes a refinement of Japan’s integrative position.