
Art-Style Dissonance: Happens semi-frequently and intentionally thanks to the Perception Filter installed on the Manager's camera and how well it works on a case by case basis.'D' presumably stands for Donator, which are Abnormality concepts pitched by the backers who helped fund the game. 'F' stands for Fairy-Tale, which are used on creatures based on real world fairy-tales. 'T' stands for Trauma, typically used on Abnormalities that are based on humanity's fears and strong personal experiences/emotions.

To elaborate, 'O' stands for Original, based on no theme in particular.
