Interesting title, it's basically what he thought when he saw her again, I'd imagine. Still, I definitely understand his shock, she looks so innocent and yet she just comes out and says she fucks four boys from her school on a regular basis. Interesting ending though. I wonder if her dad actually knows and is playing along, or really thinks she is just talking about games.
IMHO, it's implied that Keigo will "take responsibility, right?", if the need calls for it. And I personally think that Father "Knows" what Aina meant when she said rather exuberantly that Keigo *cough-cough* "pounded her good"; somehow, if he didn't approve of Keigo in that way, he'd probably be reaching for the family katana.