Deacon St. John, the gruff-voiced protagonist of Days Gone is just a man. Because this is a video game, we don't need to embrace those human frailties. Instead, we can fill him with some strange drug that makes him stronger and better in every way.
How To Increase Health, Stamina, And Focus Using A Nero Injector
The first thing you need to do is keep an eye out for Nero camps. Nero was some sort of government response unit that was trying to stop whatever event destroyed civilization as we know it. The buildings are pretty easy to spot, as they will normally have Nero written on the side of them in large white letters.
When you do find one, don't rush in, scout the area for Freakers carefully, then make your move. The first thing to do is climb on to the roof if you can, you want to disable any speakers that you can find up there. Just interact with them using the Square button to cut them down. If you don't disable the speakers, they will end up attracting enemies when you get inside the building.
Now, try the door. Sometimes it will work, but other times you will need to turn the power back on. To do this, scout around for the generator. If the generator is out of gas, you will need to find a gas can and refill it, then power up the generator.
Head for the door and go inside, and you may find a large white container. Interact with it, and it should hopefully have a Nero Injector. Now, you will be able to choose between upgrading your Health, your Stamina, or your Focus. Pick the one you want, and you are good to go.
