Now first, you must get project zomboid, and then go to the workshop, you can install THESE MODS!
Quick Kill : https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2402057349
Spawn With Gun : https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2747517727&searchtext=spawn+with
Now open up project zomboid, go to mods, activate those specific mods and then select New Game...

Go on any gamemode you want, most recommended is Custom Sandbox.
Select Veteran (that gives you a gun!) and pick some negative traits until you can create your character.
Create your deadly friend however you want!

First, load your gun with the necessities it requires. Then right click it and press Suicide, you will be prompted to select Yes or No to suicide, pick Yes so you will finally end your miserable life.