This study investigated how Japanese curricula represent functional relationships through the lenses of quantitative and covariational reasoning. Utilizing both macro and micro textbook analyses, we examined the tasks, questions, and representations in the Japanese elementary and lower secondary course of study, teachers' guide, and textbooks. Findings showed that, starting from the 4th grade by the end of 8th grade, Japanese curricula focus on iteratively improving learners' quantitative and covariational reasoning gradually raising up to continuous covariation level. This pointed out that Japanese curricula have a spiral nature in the learning of functional relationships involved in proportional and linear situations. We discuss the implications of findings for teaching, learning, and teacher education. [For the complete proceedings, see ED657822.]