I am fairly certain there are (or was, anyways) higher octane blends than this which come in the boxes. There are way more than just 2 kinds of shouchu which come in these boxes. The kind we (regrettably) drank in college was 18%-23%, and came in what more closely resembled quart sized milk cartons, and it had little boxes as well of the same stuff.
Alcohol laws are more strict now than back then, so a lot may have changed. Alcohol vending machines are all but extinct. So too might be the stronger juice box shouchus.
