Actually, this trip has another purpose. Ken-chan secretly loved Tanihara Nozomi but had no chance to show it to her.
He immediately asked his close friends, who are now husband and wife, for help. So they organized this trip so the two of them could get closer. Nozomi and her husband helped Ken-chan achieve her goal.
But that night, witnessing Ken-chan making rough love with Nozomi aroused Nao. She can't stop thinking about Ken-chan and when Ken-chan accidentally goes into the girls' bathroom, Nao holds him back and uses her beauty to seduce him into ejaculating repeatedly inside her.
And when she returned, Nao was pregnant, and that pregnancy was most likely Ken-chan's...
