Dark Arms: Beast Busters is an action role-playing game released by SNK for Neo-Geo Pocket Color in 1999. It is the follow up to the SNK arcade shooter Beast Busters. Dark Arms features a girl, Meghan Loughlin, whose job is to defeat and contain an outbreak of demons and act as a mediator between this world and the next. The game is unique in that you can collect the spirits of the various demons and zombies you fight in the game with a gun known as The Catcher. You can, in turn, use these spirits to feed other weapons to evolve them into more powerful weapons (Handgun into Sub Shotgun into Shotgun, etc.).
Source: Wikipedia, "Dark Arms: Beast Busters," available under the CC-BY-SA License.