Background and Objectives: The human–nature relationship in the curriculum can contribute to shaping students’ attitudes, sense of responsibility, health awareness, biosecurity, and territorial sustainability. Given the potential of the Defense Readiness course in addressing these issues, the present study aimed to explore the components of the human–nature relationship in the intended and implemented curricula of upper secondary education.Methods: The study employed a mixed-methods approach. Semi-structured interviews were conducted with 18 experts, textbook authors, educational group leaders, and experienced teachers, and the data were analyzed using thematic analysis. Subsequently, the content of the Defense Readiness textbook for the 1404–1405 academic year was analyzed, and the implemented curriculum was examined from the perspectives of 209 teachers using a researcher-developed 45-item questionnaire. Quantitative data were analyzed using the one-sample t-test and Friedman test.Findings: Fifteen main components were identified. The content analysis yielded 1,210 codes, with healthy nutrition and human biological health receiving the highest level of representation and responsible and nature-based tourism the lowest. In the implemented curriculum, the dimensions also showed different patterns in relation to the midpoint of the scale.Conclusion: The findings highlight the need for greater attention to content balance, teacher preparedness, educational objectives, and supporting resources.