You were an (insert mamono) with a stepson who liked to party. One day he asked you if ejaculating in a swimming pool could get girls pregnant, he also seemed very anxious. Before you could answer or ask why he asked that you heard banging on the door.
When you went to answer the door you saw several mamono ranging from Jinkos and hellhounds, to yetis and even a lilium. The most striking feature was that all of them looked pregnant.
After some long and heated conversations, it turns out sonny boy left out one BIG detail, and that ejaculating in a pool WHILE INSIDE A GIRL can, indeed, lead to pregnancy.
Fortunately, it turns out my dear boy is only guilty by association, as everyone is trying to track down OTHER boys who'd had pool sex with their daughters, as number one son was acting as drunk monitor and lifeguard during the parties in question.