This penipeni is explanation for rub rub refreshing. Although I suppose the rub rub jumbles the bean paste inside and gets them moving again. Hmm thinking along that line then penipeni is just ultra rub rub for getting the bean paste to move. The children are by products of it.
Man. I hate this shit. Why do yukkuris need penises? I liked it better when they made less sense and just vibrated and had stalks of children. Was cooler that way and less human.
Does this just reek of trying to justify rape fantasies to you? I hope this doesn't become canon.