If he's been a little sis fanatic since before Chihiro was born i wonder this is all an elaborate ruse by their parents so he wouldn't do anything to his little sis Chihiro...
@KajurN
...you are aware that they're unrelated by blood, right? Their parents remarried when he debuted as an author, so he's only known Chihiro for three years and they have yet to establish why they're hiding it from him in the manga.
Its weird that their unrelated by blood but their hair as the same shade color and... shine? Idk what its called but their hair looks really close, I usually notice that only on related characters .