Responses
From what I've observed, I don't think the loli/shota thing started the way they are now. In asian culture, being youthful is the ideal. That's why a lot of the fashion trends are geared around youth in Japan and pretty much 90% of the anime/manga media is about kids in school (any level, but it's always school). So what started as a "the younger you are the better" got sexualized like pretty much everything and we have what we have today.
I don't think most loli or shotas in general manga are meant to play off the whole sexual aspect unless they are really explicit about it. Most of the time it's comic relief.
just my opinion on this but I don't find the childhood friend funny. Rather, I find her rude and annoying, especially at first. It bothers me less when Kousaka warmed up to her but at the start, I really though she was being extremely insensitive.
I don't like the loli jokes. Call it what you want pedophilia seriously puts me off. I'll never get this loli/shota thing Japan has...
Otherwise it was... weirdly fun and good. Not bad at all!