The "antagonist" of Rockman 4
, Dr. Cossack, makes a guest appearance in Rockman 8
. But wait! Before you go screaming about "I already beat that game! Where is he!?", he doesn't appear in the game, but in a manga series BASED on Rockman 8
that was released in Japan! Cossack's daughter, Kallinka, also makes a quick appearance in the manga.
In Japan, a doujinshi manga (fan-created manga) of Rockman 4
is available. It follows the game's plot more or less straight through, but it's missing two boss encounters from the game: one from Cossack's citadel (the Wall Walkers), and one from Wily's castle. The manga was published by the manga label BomBom, and it's a rather rare find.