I really love the idea of a reverse siscon. Normally, it's the older sister who is creepily in love with their younger sister. For example, Akane from Yuru Yuri. This time, it's the younger sister in love with the older sister. Ironic, isn't it?
the kinder eggs we get here, isn't even an egg. you open the package and the chocolate is on one half, and the prize is on the other. here as in alaska USA, and they are separately sealed within the egg
Yuri being rather stronger than she looks is just one of those running gags; but she's rather more possessive than "protective" of her friends and at best takes a while to warm up to new people in her relationship matrix as eg. Nemo could attest - and Shizuku has the superpower of pissing off other girls pretty much just by existing, so...