There's a lot of discussion in the Wikipedia article saying that you can't compare rates internationally. Please be a bit more careful with statistics.
In England police recorded numbers for crime are not seen as statistically sound.
> In January 2014 the UK Statistics Authority published an assessment of ONS crime statistics. It found that statistics based on police recorded crime data, having been assessed against the Code of Practice for Official Statistics, were found not to meet the required standard for designation as National Statistics.
We can't compare the numbers between Japan and the US because we don't know what definition of rape is being used in each country (and for the US that definition is different for every state).
We don't know if there are cultural things that change how many people report a rape to police. We don't know if police record every report.