Life Force

Life Force is the North American name of the game which is a spin-off of the original Gradius game. It began life as an arcade game where it was released in Japan under the name Salamander (沙羅曼蛇). It was brought to the United States as Life Force. It was then re-adapted back to Japan under the same new title with a more organic theme. For more information about the arcade game and its various versions see the Salamander guide.

This game was converted for many popular systems, including the NES. In Japan, the Famicom conversion of the game retained the original title of Salamander, while outside of Japan, it was released as Life Force. While this conversion retains most of the contents of the arcade version, some changes were made for this release. Like the arcade game, it contains two-player cooperative gameplay, both horizontally and vertically scrolling stages, and the ability to resume play right where your ship was destroyed. Unlike the arcade game, it does not have the simplified power up system. Instead, it returns to the Gradius style power-up system.

In addition to this modification, stages were rearranged, and some stages were entirely redesigned. The arcade's fourth stage is now the second stage, and the two stages that consisted mostly of space have been replaced with new stages, one of which continues the biological theme introduced in the first stage. Many aspects of the existing stages were simplified to run smoothly on the NES hardware, but the look and feel of the game is quite faithfully retained. The game was later re-released on the Wii Virtual Console in Japan at the end of 2008 and in the United States at the start of 2009.

Story
A large creature named Zelos (possibly the serpent often pictured on the game's cover art) is preparing to swallow your planet whole, and you must stop it from the inside out.