Boktai: The Sun is in Your Hand

Hideo Kojima, the man that's most known for bringing the Metal Gear Solid series to life, has come up with an extremely ambitious idea for the Game Boy Advance: harness the energy of sunlight for a videogame. Enter Boktai, a vampire-hunting action and adventure game that not only encourages players to get outside and play in the fresh air...it almost requires it. Utilizing a special cartridge with a built-in a sun sensor, the amount of sunlight outside the game determines how much sunlight shows up in the actual adventure. And since the player's gun is actually fueled by sunlight, the more sunlight you can get the stronger and more capable you are in the game.