What law is he genuinely breaking in the first place? I don't think it's illegal to keep a minor in your home with their consent. Taking her in is what people should have done. As well as that, I believe that the MC's path right now is create a place where Sayu can be comfortable and rehabilitate from what she did before, and once she overcomes these things, she leaves. Also, who wouldn't want to help a struggling girl thats homeless? The fact that he can come home to miso soup is only an afterthought.