Reason for why 3 stars... 1.) we don't really know if they're blood related... 2.) they're parents often leaves them alone with each other...  (if they're blood related their parents just thinks they're pretty close... While if they're not then the reason why their parents keep leaving is that they're giving them an okay...) Let's just hope they aren't blood related... And also this is a manga/comics that we're talking about so we also don't know her actual age...