"When he get that feelin', he want "J.K." healin'. "J.K." healin', oh baby. Makes him feel so fine. Helps to relieve his mind. "J.K." healin' is something that's good for him."
(J.K. means Joshi Kousei 女å高生, "high school girl,", of course)
But Seriously Though, I didn't see no protection being used, so here's hoping Aino-chan knows her cycle well enough, otherwise she might (a-hem) not remain a student for long (in which case, Mister had better "take responsibility, right?") And there's also the matter of the Age Of Consent - one wrong move and Mister's "ass is grass" with the law.
Based on the fact that she lives next door I assume her parents are cool with him "Taking Responsibility". She was waiting there pretty late and they weren't exactly quiet.
IIRC last time I looked up the subject, the Age Of Consent restriction in Japan can be (a-hem) waived, as long as the parent(s) or guardian(s) of the person(s) under said age gives their consent (usually it must be given in writing) to the underage person(s) engaging in "this and that" ... but it's not as simple or straightforward as I've just stated it. Well, anyone who wants to can look up the subject in detail for ... er, "research purposes".
The best kind of healing...8 whole pages of lovely coloured goodness!
I must say though, I'm quite curious about the nature of their relationship and how it came to be...