Every time I read this I love it but I'm so afraid someone is gonna hear them using the word "rental" and think it's child prostitution or something. I can't help but think her bio brother would totally try to get this guy arrested like that...
I also really hope they never, ever become a couple, even if enough years pass for the age gap to be unobjectionable. I like the manga for what it is, two people forming a sibling bond and a kind, young girl learning that there are good people in the world.