Demonstar is an 1997 Indie vertical scrolling shooter shareware computer game was designed and developed by Mountain King Studios, Inc. and published by ionos, inc. in 1997. It is was the first original DemonStar series of top down vertical scrolling shooter computer game. The version was also 3D parallax air and ground was published ionos, inc. The game shares many similarities with the Raiden series. DemonStar features various power-ups, including smart bombs and other power-ups which modify the types of projectiles that the player's ship fires. The full version of the game features 18 levels. At the end of each level is a boss ship that the player must destroy. DemonStar was very successful in the shareware computer game, despite Mountain King Studios initially addition to the original game, two additional titles have been released: DemonStar Secret Mission 1 and DemonStar Secret Mission 2.

The Terran Fleet is developing a new prototype starfighter, the RaptorX, and the player is a test pilot of that prototype. Suddenly, the Xidus Armada Fleet, the Terran Fleet's arch enemy (ever since Galactix), launches an all-out surprise attack on the Terran Fleet that catches them with their guard down, destroying all Raptor fighters in the process, save the few RaptorX prototypes which were away being tested. Now the player must battle through the Xidus Fleet alone, destroy their ultimate weapon, codenamed the DemonStar, and save the rest of the Terran Fleet.