Comprehensive Sexuality Education has been acknowledged globally for its role in advancing young people's Sexual and Reproductive Health and Rights. Yet, notable variation exists in definitions and interpretations of what comprehensive means, exposing tensions between international and local values and agendas. This research focused on the situation in Japan, which is largely perceived as 'lagging behind' international standards in terms of its sexuality education programming. We aimed to explore the degree of comprehensiveness and variation within Japan's national and regional sexuality education curricula, using UNESCO's "International Technical Guidance on Sexuality Education" as a benchmark. Quantitative and qualitative curriculum analysis was conducted using an Excel tool. Findings revealed greater comprehensiveness and regional diversity than previously reported, although significant gaps persist regarding more explicit sexual subject matter and critical gender perspectives. These results illustrated promising progress towards comprehensiveness, even in the conservative educational environment of Japan. Nonetheless, in aspects such as rights, Japanese educational discourse differs substantially from that of the wider international community, contributing to the perception that the country's sexuality education programme lacks comprehensiveness. This calls for greater cultural responsivity within the Comprehensive Sexuality Education agenda, albeit without compromising its core values and safeguarding of young people's sexual health and rights.