A young Minato asking Jiraiya what a period is after fighting Kushina during the Chunin exams because she had to forfeit due to having her first one and not knowing how to deal with it.
The letter correspondence between Kushina and Minato at the start of chapter 20.
When Minato's friends set him up with a prostitute to end his virginity and she turns out to be an assassin. He's relieved and says as much, because that sort of thing he can deal with!
