The school arc is future plot development, all of the people in his ever expanding circle at the Academy will one day need or help out Rudy with big stuff and inventions.
@DirkHardpeck She was previously a rich snobbish girl who only thought of superficial things and didn't have any depth to her character. Would you want to be friends with someone who doesn't even know the basic knowledge of her own country situation and just spends money all willy nilly and...
'This manga is about an isolated restaurant where you tell the chef your worries and he cooks up some seafood for you. The owners of the restaurant are a black cat and a witch.' isn't it supposed to be 'she cooks up' since the cook is the witch?
@mrmm Shirasaki Kaori is the first girl who loved Hajime before all of this had started, the healer.
https://myanimelist.net/character/129883/Kaori_Shirasaki
I think the reference is her practicing how to speak in the previous extra, the other one that comes to mind is when she was eating the school lunch where she also said 'delish'.