Ganpuru: Gunman's Proof

Action-adventure with slight RPG elements (buying and upgrading weapons, etc.) set in Wild West. While featuring traditional dungeon-crawling and many enemies to dispose of in real time combat, the game doesn't equip you with standard medieval swords, but with pistols, shotgun, machine gun, and even a flamethrower. Your weapons have infinite ammo. You can duck to avoid the alien monsters' fire, and perform special attacks with various types of weapons.