Monster World IV (モンスターワールドIV) is currently the last game in the Wonder Boy franchise, and was released for the Sega Mega Drive exclusively in Japan in 1994. Despite its name, it is actually the sixth game in the series, however Japanese continuity discounts the original Wonder Boy and Wonder Boy III: Monster Lair as being part of this series due to their different gameplay styles.
A departure from previous games, the player now controls a young girl named Arsha (Known as Asha in the English translation), instead of "Wonder Boy" or Shion from Wonder Boy in Monster World. This, and the large amount of text, may suggest why the game was not released outside of Japan, however a fan translation by translation groups Demiforce and DeJap surfaced in 2002. Monster World IV is also playable via the GameTap service (which is available in the west), though the game was not translated.
Monster World IV has also been released as part of the Wii's Virtual Console service, which marks the game's first English release. Its copyright notations in the game's Operations Manual indicates that it was to be released a year prior to its 2012 release.