SD Hiryu no Ken Gaiden 2 is the sequel to the first SD Hiryu no Ken Gaiden (and is, by proxy, a sequel to the Super Famicom SD Hiryu no Ken). Gaiden 2 adds four new characters, but is otherwise identical to the previous game. However, Gaiden 2 received an updated re-release named SD Hiryu no Ken EX that adds more options.
