Salman_Shh Doing a non-violent game can be tricky, but it can give a lot of interesting mechanics as well as strategies to make it unique. I'm not doubting on you.. ^^' But.. Imagine.. Player's gun is in fact a 'tear gas' gun that makes enemies sleep for a few seconds. You don't have a lot of bullet, just a few like one per level. You start with none, and have to reach that bullet first, then find your path and use your one tear gas bullet subtly so that you can get to the next room.
Well, just an idea ofc.. ^^'
As CreativeMind said, negociation could be very fun as well. Have you seen 'Casa Del Papel' serie? It could give you a looot of inspiration as one of their goal (ofcourse after stealing money) is to be non-violent.
Enough talk.. That's your game :P But I needed to say this.. ^^'