Disclaimer: Mai and Jounouchi belong to Kazuki Takahashi, not me.
Mornings are the easiest part of the day. In the morning, she is still half-floating with sleep, nothing more on her mind than the slow untangling of bodies and the languorous ache in her limbs and the smell of sweat and that other scent that she's never quite been able to identify but which is unmistakably Katsuya.
Later in the day there will be an infuriating amount of traffic and an even more infuriating amount of being polite to people she privately loathes, meaning that she will be tense and snappish when she has lunch with Katsuya, which will make him snappish and defensive, which will lead to a loud argument over some inconsequential thing that has somehow become dreadfully important, which means that she will return from lunch in an even worse mood than she was before, which means that everyone else around her will have almost as bad a time as she's been having (which will, perversely, make her feel a bit better), and when the day finally ends she will go home to pick a fight with Katsuya which will end with them having loud, enthusiastic make-up sex on the kitchen table. But for now she is loose-limbed and happy, and from where she is lying, it looks like a good day.