Phelios (フェリオス Feriosu?) is a 1988 vertical scrolling shooter released for the arcades in Japan by Namco. It runs on Namco System 2 hardware. A home version for the Mega Drive/Genesis was released in 1990. The game features a plot loosely based on Greek mythology. The player takes control of the knight Apollo, the god of the sun, who sets off on his pegasus to rescue his lover, Artemis, the goddess of the moon, from the dark lord Typhon.
The player controls Apollo who is mounted on the back of his winged horse Pegasus. Pressing the fire button makes his sword fire a tiny shot, while holding it down charges the sword, firing a bigger fireball upon release. Even the smallest enemies take multiple hits, so the standard shot is of little use. This game also features voice samples (in Japanese).
Source: Wikipedia, "Phelios", available under the CC-BY-SA License.