Akiha isn't the type to pout much. The fact that the expression not only sticks around, but deepens, her lower lip pushed out and her eyes lowered, makes it clear that Nico's teasing is getting to her. She grumbles wordlessly as Nico slowly undoes the buttons, taking deep breaths through her nose to keep from interrupting herself.

Nico's teeth against her ear felt good, after all, even if the pace was about a hundred times slower than she'd like. With every button, Akiha's heart races faster and faster, the anticipation building. Akiha's grumbling fades away into shallow, uneven breathing, until Nico finally pulls away from her ear and looks down at her. Akiha looks up at her, lovingly.

At least until she ruins the mood by talking. Akiha blinks up at her and then narrows her eyes, the moment completely lost. "Not on your life, Yazawa."

That's her way of letting Nico know she's in a bad mood now.