Somebody's going to say this so might as well be me as anyone else ..... Megumi did well to Hold Out For A Hiro. And that combo of wet clothing and teen hormones (plus some hitherto-unspoken mutual feelings) would ensure that nature (at least in the H-Universe) would take its expected course.
For a moment I thought her name was Megumin, although Megumin just would have blasted the door away with explosion and we would†˜ve missed out on the lovemaking bit…