
Once you're done with the mission and talk to the veteran, kill him. If you completely refuse to take your medicine, you will be told to kill everyone on sight. You can get this key much easier by simply refusing to take your medicine before the mission. The description says: “Shoots an otherworldly beam when charged,” which is pretty self-explanatory. This key will open the second door, which holds the Sword of Masters. Get near the body and loot him to grab the Master Key. As soon as you start walking, throw the object to kill the enemy before he jumps. Once that’s settled, open the door to the rooftop. When you arrive at the location of said encounter, which has two enemies in a room right before it, you’ll want to take them down using melee and save a throwable weapon in your inventory (the head statue is perfectly placed for this). In order to get here, you’ll have to go through a couple of stages that shouldn’t give you too much trouble. You’re gonna want to head to the third checkpoint, right before the final interaction with the NPC on the rooftop. The description reads: “The world is your canvas and the world is the paint.” The Prism Key enables a flashy new Prism Sword in the Government Lab. Approach them and interact once the button prompt appears to get the Prism Key.

You’ll see a dead body laying in the left corner. Once you can jump, get on top of the building nearby, and start making your way until the beginning of the level.

When you start the game (or just go back using the chapter selection screen), deflect the first bullet and then continue doing the tutorial. They all hide weapons, and unless you managed to pick any during your first playthrough, it's likely that you've missed them all. In here, there are five locked doors that require a special key for each.
