Disaster-related deaths can be classified as direct and indirect disaster-related deaths that are becoming more predominant in Japan. To reduce indirect disaster-related deaths, accurate statistics based on medical documentation are essential. However, the definition and reporting of such deaths in Japan present systemic challenges. These deaths are certified and recorded by municipalities at the request of bereaved families seeking condolence grants. This cross-sectional study assessed 755 certified indirect disaster-related deaths after the 2011 Great East Japan Earthquake in the Miyagi Prefecture, Japan, to determine whether medical documents mentioned disaster relevance. Of the 755 cases, 74 (9.8%) death certificates and 145 (19.2%) medical documents described the relevance of disasters. Relevance mentioned only in the self-reported documentation from bereaved families was 536 (71.0%). The median [interquartile range] time from the disaster onset to disaster-related deaths was 21 [7-52] days. The mean age was 79.7-years-old, and 346 (46.7%) of the victims were female. The predominant etiologies of these deaths included circulatory (32.7%) and respiratory (27.7%) diseases. The time periods of the deaths varied among the municipalities, suggesting a lack of consensus among the review committees. Establishing a medical and social consensus for indirect disaster-related deaths and recording them on death certificates is crucial for accurate disaster death data and social resilience.