Awwr...STEVE. It's good though that he's able to do things he enjoys and take things easy. PLUS BUCKY. Yuuki will be a great student for him. Gym was the class she enjoyed/did best in. :'|
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As for the fastest way to cheer Yuuki up (apart from food LMAO People know her too well)... I guess I would say getting out and about, doing things with friends. She has agoraphobia and actually HATES being alone. Especially if outside of her comfort zone. In canon that was the academy grounds (Day class ones). She can force herself out, but when human there were a few times where she legit froze up and had panic attacks. Whenever she had found herself out alone when she was younger, she had become the target of bad vampires.
Due to her history, to her embarrassment, despite being at the top of the food chain now, Yuuki still gets jumpy and uncomfortable but forces herself out. She's become comfortable/familiar enough with the main part of Kiseki- the school, hotel, the park, welcome center and shops. Before, however, she never really visited the islands due to her discomfort levels. And the only time she would wander into the forest or other sections alone was due to needing to help someone or there being some kind of need.
So I think just engaging her, being invited to do fun things together and visiting places she hasn't been to before would cheer her up a lot.