Thank you to those sharing information about the cultural and political climate in Japan to help us better understand the issue. I have a potential solution for how this problem may be resolved.
1. Don't approach this issue with the intent of legalizing marijuana. Rather, appeal to their conservative sensibilities by outlawing MORE things. EVIL things. More specifically, weeds.
2. After all weeds are made illegal, the entire nation will be on the verge of imploding due to the ubiquitous influence of sea weed across all of their cuisine. At that point, it will force them to think about what the "big deal is" between sea weed and weed.
*deep inhale*
You know what I mean, man (while trying to hold the hit in)?
*coughing*