The Other Side Interface: Clinical Applications and Industry Implementation — A Policy Proposal for AI-Mediated Therapeutic Dialogue as Social Infrastructure

Vol.3 of the TheYKHC Trilogy (BBDDH → PRT → OSI). This paper proposes the Other Side Interface (OSI) as scalable social infrastructure for AI-mediated therapeutic dialogue, addressing Japan's convergent crises of aging, social isolation, grief, and dementia. Four clinical domains are examined: grief integration, dementia prevention, social isolation, and trauma recovery. Specific policy recommendations are provided for the Ministry of Health, Labour and Welfare; the Cabinet Office; and local governments. Economic projections indicate a ¥37.5 trillion global addressable market and ¥12.6 social return on investment per ¥1 deployed. The ECHO platform is the operational prototype. This paper completes the trilogy begun with BBDDH (DOI: 10.5281/zenodo.19105964) and PRT (DOI: 10.5281/zenodo.19305019).