The broad agenda of ontological security scholarship in International Relations is to examine states’ (in)security of Self-identity and the implications for their international conduct. While ontological security may be an illusory goal, states vary in their levels of ontological insecurity, with more extreme levels producing acute defence mechanisms. Such ontological crises are therefore an important area of focus gaining increasing attention. Thus far, however, they have generally been conceptualised as ‘critical situations’: unpredictable, transient and practically resolvable ruptures of routinised practices. I argue that such a conceptualisation neglects the possibility of a more fundamental, long-term crisis of Self-identity, which I term perpetual ontological crisis. Such crises stem from inherent contradictions within dominant constructions of identity that may have always existed – rather than exogenous shocks to a hitherto secure Self – and are therefore irresolvable within the bounds of those constructions. I develop the example of nation/state incongruence: when a state’s territorial boundaries do not accord with the national spatial imaginary dominant in that state, resulting in an inherent and enduring contradiction. I then illustrate these contentions with a case study of South Korea, whose borders have never matched the imagined spatial bounds of the Korean nation. To demonstrate the implications of this crisis, I conduct a discourse analysis evidencing a nexus between enduring ontological anxieties concerning Korean division and South Korea’s persistently antagonistic relationship with Japan. In doing so, this article has important implications for how we understand ontological crisis and offers a novel account of its empirical case.