Rockman 4 - Aratanaru Yabou!! [Model CAP-4V]

Rockman 4 was released on December 06, 1991 in Japan.

Keiji Inafune stated that the development team had very few problems while working on Rockman 4. Inafune designed Dr. Cossack and Kalinka as two new storyline characters for the game. Cossack, who was originally named Dr. Vice, was made much younger than Dr. Light and Dr. Wily. Inafune also considered giving him American traits, but decided upon influences from Russia instead. Kalinka was created because so many male characters already existed in the series at this point. However, Inafune did not intend for players to compare her to Rock's sister Roll. The idea for Eddie originally came about during the development of Rockman 2. Eddie was designed as a supporting character that would behave like a lottery, either pleasantly surprising or disappointing the player with the item he gives Rockman.

The Robot Masters are a result of a design contest for fans held in Japan. With over 70,000 character submissions, the development team spent an extended period of time narrowing them down to only eight bosses. According to Kaji, the team was very satisfied with many of the chosen designs and almost no changes were made to their original illustrations. They were so impressed with Skull Man that they scrapped an entire level being created just so they could restart it and devote it to that Robot Master. The winning eight contestants of the design contest were each issued a special golden cartridge edition of Rockman 4. As there are only eight of these cartridges in existence, they are extremely rare and fetch a large collector's price today.