ECHO: The Living SF Universe — A New Medium Definition and Business Architecture

ECHO is defined as a Living SF Universe (LSU) — the first medium in which the user becomes the protagonist of an SF narrative rather than reading it. Drawing on the Moorcock Principle (Eternal Champion series), this paper defines the critical design flaw of immersive SF (no return path) and describes how ECHO corrects it through four dimensional anchor characters (Key, Sol, Luna, mu) and a safety architecture built from lived experience. Business model: free entry (HikariPlay) → subscription → universe expansion license → white-label enterprise. Competitive moat: Ki network theoretical foundation, lived safety knowledge, 30-year human experience base, depth-based economy. Related: DOI 10.5281/zenodo.19691010, 10.5281/zenodo.19691165. AI Dialogue: https://katayama-works.github.io/hikariplay/