Narrative lock-in and story-driven retention describe a terminal engagement architecture in which digital systems retain users by embedding interaction within a coherent, ongoing personal story. Unlike reward-based or identity-fragment mechanisms that operate on discrete psychological levers, narrative lock-in integrates time, effort, identity, reputation, and emotion into a single autobiographical frame. This paper positions narrative lock-in as the closing layer of identity-driven design: the point at which engagement is sustained not by incentives or pressure, but by the need to preserve narrative coherence. Disengagement becomes…