One thing Marlene loves about Niki is his eyes, when he smiles his eyes light up and Marlene has to concentrate to even breathe.
Marlene loves it when Niki wears his sunglasses but every time he looks or talks to her he takes them off so she has the chance to see his eyes when they communicate with each other. She literally goes weak in the knees when he stares at her and smiles.
Niki loves Marlene's hair. Loves playing with it, running his hands through it, and washing it when they take showers together.
The reason why Marlene kept her hair up after she met Niki was because he loves seeing her hair down and out of the bun so whenever her hair is down it's when she's around him. She rarely has it down when Niki is not in the vicinity and doesn't show her hair down in front of anyone else.