So i think the way both kids reacted towards the kiss is how they see their parents act. Nagi and Kotone are very affectionate so i’m sure Yua sees them kiss a lot and thinks that’s the way to show affection. In Kagetora and Wu’s case, Tora is usually standoffish when Wu shows affection so that’s why Meiran slapped Yua. In any case, both kids just reacted the way they see their parents act XD
So i think the way both kids reacted towards the kiss is how they see their parents act. Nagi and Kotone are very affectionate so i’m sure Yua sees them kiss a lot and thinks that’s the way to show affection. In Kagetora and Wu’s case, Tora is usually standoffish when Wu shows affection so that’s why Meiran slapped Yua. In any case, both kids just reacted the way they see their parents act XD