Because I am your little brother, of course.

[After all, you're his niisan, Natsuno.]

I want to be able to figure you out so I know what you like and what you don't, so I don't do anything you don't like or that would make you angry and go far away. And so that I can do what you like so you can be a bit happier or a bit more fine whenever you're unhappy or not fine.