This missable achievement is unlocked for beating the entire game without ever using your gun, on people or otherwise. You'll also unlock Peace and Coffee and Chainsaw Dance on this playthrough.

Of course! Every lock has a key, and nobody has to die by your hand. Some puzzles get slightly more complicated, though.

When you right-click, Aino's backpack appears on-screen. It's not easy to see, but below the compass, you should see three bullets. If there's any less than three, then you've used your gun and need to load an earlier save.

When you reach the end of the credits.