Abstract: Under the context of ongoing sea level rise, the response of beaches along fixed shorelines has become a critical issue in coastal evolution studies. The classical Bruun rule, based on the equilibrium profile assumption, suggests that natural beaches can adapt to sea level rise through landward translation. However, where hard coastal structures such as seawalls are widely constructed, the restriction of shoreline retreat raises substantial debate over whether and how beach morphodynamic adjustment fundamentally changes. Some studies argue that seawalls intensify passive erosion by enhancing wave reflection and localized scour, whereas others indicate that, under specific hydrodynamic and sediment supply conditions, seawalls may induce localized accretion or lead to a new dynamic equilibrium. In response to these divergent views, this paper systematically reviews the driving mechanisms of sea level rise, the spatial classification and relative positioning of seawalls, hydrodynamic-–sediment coupling processes in front of seawalls, and the applicability and limitations of predictive approaches such as the Profile Translation Model (PTM). The synthesis suggests that seawalls constrain landward profile translation, redistribute sediment budgets, and concentrate nearshore erosion, resulting in scenario-dependent and region-specific beach responses. Future research should strengthen long-term field observations and integrate numerical modeling with scenario analysis to establish a comprehensive assessment framework for fixed shorelines, thereby supporting optimized coastal protection and beach nourishment strategies.