What Lies in the Multiverse

You can get this when you reach the city, when you first enter the area with the casino. In front of the 2nd newsstand, there's a grey cat sitting on the ground that you can interact with. Pet the cat, and your character will must about their pet cat, Erwin. A very brief cutscene will show Erwin enjoying his time with your character gone, and just after that the achievement will pop.