Phelios is a vertical scrolling shooter that was released by Namco in 1988 only in Japan. It runs on Namco System 2 hardware and was never released in the United States due to the bondage/torture scenes that Artemis went through between each stage, similar to those in Namco's own Rolling Thunder. While no nudity is shown, the scenes were somewhat "strong" to be shown on a video game back during the game's era.
Story
The game's plot was based on Greek mythology and also used the familiar theme of saving the princess from evil. In this case, the princess is Artemis, goddess of the moon, and the evil is Typhon, one of the Titans (specifically, the one that Zeus dropped a mountain on). The player controls the heroic Apollo, god of the sun, who must ride the legendary winged horse Pegasus through 7 stages in order to rescue Artemis, who is depicted as his lover (although in the myths they are actually twins), and defeat various other Greek mythological characters such as Medusa, Antaeus, Scylla and Cerberus.