These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Kokoro Library
Growing the Beard: The series gradually becomes more serious, which leads to a lot more depth in the plot and characterization.
Moe: The sisters proper (especially Kokoro), but Hikari really takes the cake.
Wangst: Kokoro is very distressed when her first customer doesn't return her library book.