Stigma is what is classified as pieces of equipment you will find throughout Mobius. Remnants left behind from those that departed from Miyabi take the form of thoughts that you can attach as an Attack, Defense, and Amp slot. You'll actually acquire plenty through your journey around Mobius in the form of locked and unlocked Stigma chests you'll see in the areas, or through drops from enemies. There is no way to increase drop rate from enemies, which is a shame given you'll need a handful of Stigma to satisfy some Traumas later on, but don't worry about this trophy any; it'll come naturally through progression.