In recent decades, interdisciplinary learning has become a central focus of global educational reform, with STEAM education emphasizing the integration of science, technology, engineering, the arts, and mathematics. Japan, however, has pursued similar ideals since the 1990s through Integrated Expression Activities, a curriculum model linking music, language, art, and social learning. Rooted in constructivist and humanistic pedagogy, this approach positions expression not as a performance but as a collaborative process of meaning-making, uniting creativity and well-being in the classroom. The present study aims to reexamine the evolution and educational significance of Japan’s Integrated Expression Activities, focusing on how music functions as a bridge between disciplines, cultures, and learners. It explores how such practices can contribute to the global discourse on STEAM education and the ISME 2026 theme, Unity in Music Education: Building Bridges for All. By connecting Japan’s long-standing model with international perspectives, the study identifies ways music can revitalize interdisciplinary learning and address declining student motivation revealed by PISA 2022. Adopting a design-based and qualitative approach, the authors conducted research across multiple elementary and junior high schools designated by the Ministry of Education as research and development institutions. They collected data through classroom observations, interviews, and documentation of interdisciplinary projects involving music, language arts, and visual design. These materials were analyzed using thematic coding and triangulation to identify patterns in creative collaboration, motivation, and inclusion. Findings indicate that music-centered projects promote autonomy, empathy, and sustained engagement by activating multiple intelligences and providing diverse entry points for learners of different abilities. The study further reveals that music serves as an integrative medium connecting analytical and emotional learning, enabling students to construct meaning collectively. By situating musical creativity at the heart of inquiry-based learning, schools foster a sense of community, inclusivity, and purpose. The study concludes that music education can function as a unifying language across disciplines and as a model for inclusive, human-centered STEAM learning. It recommends broadening the “A” in STEAM to encompass the arts, humanities, and ethical imagination, reaffirming music’s potential to bridge cognition and emotion, as well as individuality and community, thereby building bridges for all.