China's behavior regarding the Senkaku Islands has evolved from civilian fishing vessels entering territorial waters around the Islands to military vessels showing force in the region. Japan's usual response to China's behavior had been non-aggressive and proportional to China's actions. Such use of diplomacy, combined with minimal improvements to defense capabilities, can be labeled as cooperative engagement. But China's recent escalatory behavior has caused the Japanese government to change to a competitive, hard-hedge form of engagement, with greater focus on defense capabilities than on policy. This study argues that individual Japanese political leaders, domestic constraints, and international law have encouraged this moderate but significant shift of Japanese Senkakus policy toward more aggressive engagement. I. INTRODUCTION * A. SINO-JAPANESE CONDITIONS * 1. Chinese Encroachments * 2. Benign Interactions? * 3. Japan's Institutional Interactions * B. DOMESTIC POLITICS: INTEREST GROUPS AND POLITICAL LEADERS * C. DOMESTIC CONSTRAINTS ON MILITARY POWER * D. INTERNATIONAL LAW * E. CONCLUSION * II. POLITICAL LEADERS * A. KOIZUMI * B. ABE * C. ISHIHARA AND NODA * D. CONCLUSION * III. DOMESTIC CONSTRAINTS * A. CONSTITUTIONAL REINTERPRETATION * 1. Gulf War (1990) * 2. Anti-terrorism Special Measures Law (2001) * 3. Iraq Reconstruction (2004-2006) * 4. Collective Self Defense * B. NATIONAL DEFENSE PROGRAM GUIDELINES * C. CONCLUSION * IV. INTERNATIONAL LAW * A. INTRODUCTION * B. CHINESE PERSPECTIVE * C. JAPANESE PERSPECTIVE * D. TERRITORIAL CASE STUDY * E. CONCLUSION * V. FINAL CONCLUSION