Bitasen

The Japanese populance widely despised them, giving these coins the name Bitasen (鐚銭) or "bad metal" ("Bita").

[1][2] By the 13th century these coins had replaced commodity money as currency after the Kamakura shogunate's initial reluctance gave way to approval.

[2][3] While sources agree on the Muromachi period as a starting point for "bitasen"/"toraisen" co-circulation there are differing opinions on an exact date.

[3][4] By definition, the word Bitasen (鐚銭) translates to "bad metal" ("Bita") or poor-quality coins with worn surfaces.

[2] Bitasen were frequently no longer accepted at their face value due to a practice called "erizeni", in which they were sorted out in favor of "toraisen".