A first-person shooter game where you are the only one with a gun and everyone else is kind to each other. If you shoot someone, their whole life flashes in front of your eyes. You find out they were a good person and get to see all the good deeds they did. You also get to see all the mourning and pain you created.
You as the main character show up fully armed as you would in any other shooter game. Only the world is full of kind people and there are no situations that warrant any shooting. You can talk to people. Sometimes they ask for your help. You can offer to help them do something. I haven't thought the plot through yet.
The game is basically a trap. You have all these guns. Occasionally, you see someone that looks stereotypically threatening (but really isn't). If you shoot them, you find out that they didn't deserve it. You eventually realize that there is no need to walk around with all the military gear because there are just normal people everywhere. Just because you have the power, do you have to use it?
A lot more thought can be put into this concept and make it a fun game with a good story. The guns/trap can be added as an extra lesson.