A Toy Model of Cross-System Readability and Misreadability under Divergent Histories develops a minimal simulation-oriented model of how one system may partially reconstruct, or misreconstruct, the expressed regulatory significance of another system under divergent histories. The report opens the cross-system stage of the phenomenological branch by extending the preceding intra-system simulation cascade into a two-system reconstruction setting. The paper does not introduce a theory of empathy, communication success, semantic understanding, theory of mind, or direct access to another system’s experience. It also does not activate the reserved qualitative-space objects for formal cross-system mapping. Its purpose is methodological: to show how cross-system readability can be approached as a proxy-constrained reconstruction problem rather than as transparent access. The model represents System A through variables for propagated symbolic divergence, identity-bounded continuation-width, and expressive clarity. System B is represented through historical alignment with A, grounding access to A, overload, and dominant interpretive prior. Misreadability is modeled as a reconstruction-error proxy, while readability is defined as its complement. The simulation shows that readability is high when A-side divergence is low, A-side continuation width is broad, historical alignment and grounding are strong, and B-side overload and interpretive dominance are low. Misreadability becomes reachable when alignment and grounding are weak, B-side overload and dominant priors are high, and A-side expression has already been transformed by divergence or narrowing. A grounded-feedback scenario demonstrates that stronger alignment and grounding can reduce misreadability into a partial readability range. The central contribution of the report is to show that cross-system readability is partial, mediated, and constrained by both source-side and receiver-side conditions. Misreadability can arise from A-side divergence or narrowing, B-side overload or dominant interpretive priors, or weak alignment and grounding between systems. At the same time, the model preserves the non-inevitability of misreadability: under the sampled conditions, readable and partial outcomes remain structurally available. The report provides a controlled bridge from the prior intra-system cascade toward later simulations of feedback loops, repeated cross-system interaction, qualitative mapping, multi-system readability, institutional and human–AI readability settings, and asymmetric misreadability under unequal grounding access.