Japan ranked as the fourth largest destination for Indonesian Migrant Workers (IMWs), with a total of 14,543 workers in 2025. Despite the existence of bilateral agreements and legal frameworks, protection challenges persist, demonstrating that regulatory compliance alone is insufficient to ensure migrant worker protection. This research uses qualitative methods on literature analysis to analyze how multi-actor cooperation can strengthen the legal protection framework for IMWs in Japan. Reports from Indonesian law enforcement authorities and U.S. Embassy & Consulates in Indonesia highlight trafficking and exploitation cases involving IMWs in Japan, indicating misuse of formal migration schemes and gaps in enforcement and protection. In addition, Serikat Buruh Migran Indonesia (SBMI) recorded 68 complaints involving IMWs in Japan, including certification gaps, weak legal implementation, and wage disparities, which increase vulnerability to labor exploitation. The Indonesian government enacted Law No. 18/2017 concerning the protection of IMWs. The government is also taking legal action against two former directors of a polytechnic in Indonesia in connection with facilitating the exploitation of human trafficking victims in Japan. Conversely, the Japanese government enacted the Labor Standards Act and the Immigration Control and Refugee Recognition Act. Beyond state initiatives, this study underscores the importance of non-state actors in bridging the protection gap. SBMI plays a central role through policy advocacy with the Indonesian Ministry of Migrant Worker Protection (KP2MI) and international organizations, providing case assistance and campaigning IMWs protection. Professional legal organizations such as DePA-RI have provided pro bono legal assistance to IMWs in Japan, including legal coordination with Japanese lawyers in collaboration with Indonesian diplomatic missions. This study concludes that the protection of IMWs in Japan increasingly reflects a multi-track diplomacy model, in which state and non-state actors collaboratively seek protection for IMWs in Japan alongside legal protection from both the Japanese and Indonesian governments.