Responses
Right! what if shu decided to celebrate the beginning of holiday with his friend and come home really late (even if it is the same day). I really don't think that leaving a child alone at home for few hours is safe. I have a soon-to-be two year old nephew, if you let him play alone, he will go around exploring the house, the kitchen etc. One time I caught him trying to turn on the gas!
Some may argue that chiho knew better than that but chiho is still a child.

This gonna be a very unpopular opinion on my part and please don't attack me for voicing this. I think that both chiho and shu parent are irresponsible by just dumping chiho on shu without any warning. In chap 1, upon coming home, shu found that there is an unknown girl inside the house - He never even meet her before!
I''m sure they're both nice ladies but I think if you're gonna entrust a kindergarten to a high school student at the very least you should have tell him about it. And for a very long time too! we are not talking about babysitting a child for few hours but a freaking 3 months long!
Shu was given piles of how-to step-by-step instructions written on papers to help him but that will only be a small help on his part. If this method really work, then everybody can just print similar instructions from internet and be a babysitter.