My God...her breasts and buttocks are enormous. Ahem that aside.
Any parent-child activity must really hurt for Naoto to see. Or even hearing them talk about what their parents are doing for them. Reminds me of Jun from Ai no Senbiki. Both have to witness other kids having good bonds with their parents while not experiencing even a fraction of it themselves. And both have an onee-san who's come in to the picture to fill that void and more.
Also, Naruko is really thorough. Not just the hat to hide her face but also wearing gloves. Even the little thing she did at the end of the chapter. Throwing the pen distract the teacher.