Exerion

xerion (エクセリオン Ekuserion?) is a vertical shoot ’em up released by Jaleco in 1983 and licensed to Taito for distribution in the United States.

Screenshot from arcade version
Exerion is a shoot ’em up game featuring parallax effects and inertia simulation, something notable for 1983. The player travels around strange scenarios shooting aliens. The player has two types of guns: fast single shot (limited) or slow double shot (unlimited).

In 1984, along with the MSX1 port of the original, a sequel was released titled Exerion II: Zorni for the MSX1, with similar gameplay to the original. There were plans for an NES release of this game. In 1987, the game was followed by the semi-sequel titled Exerizer, also known as Sky Fox.