Much of OTC sales comes from selling "DORINKU-ZAI", a vitamin/sugar/caffeine/ethanol mixture, and other vitamin products.
A word of caution: Acetaminophen (Tylenol, etc.) is not generally available as OTC in Japan. There are some children's Asprin substitutes (e.g. Shouni-you Bufferin C-II).
To be continued . . .