After thinking it over for a time her comment started to worry him. Obviously Naruto couldn't actually be pregnant but perhaps what she said wasn't entirely without content. After all, what if she'd just gotten her pronouns confused. That worried Shikamaru immensely but a few oblique references around Naruto revealed that he knew absolutely nothing about sex. A bit odd considering his remarkable ability to turn himself into a girl with a non-illusory henge (something Shika needed to investigate at some point) but it meant that he could put off breaking Naruto's legs until later.
As weeks passed Shika continued to keep an eye on him, just in case. Naruto was an overenergetic idiot but the fact remained that he was nearly two years older than them and he didn't want Naruto taking advantage of his innocent sister. Thankfully all of Naruto's amorous attentions seemed to be focused on one Sakura Haruno, civilian kunoichi trainee.
Shika was actually getting ready to give up his intermittent surveillance of the boy when Keiko got it into her head to drag him to kunoichi class after school. Shika found it hard to believe that the troublemaking preteen was willing to give up his afternoon to go to a class about flowers or whatever but trumping that was the fact he didn't immediately get caught. Truthfully Shika wasn't sure anyone even suspected besides himself and his sister since so far as he could tell Naruto's ANBU detail didn't follow him during classes.
Naruto's disguise was… convincing, he had to admit. Unlike the terrifyingly sexy henge he used during the last quiz this one was more subdued. The red hair and vibrant green eyes were eye catching but other than that there was nothing 'Naruto' about her. No birthmarks on her cheeks, a fairly shy attitude, and only the most minimal of curves made her blend in when Naruto typically tried to do exactly the opposite.
Worried that Naruto would use that new guise to get closer to his sister Shika had chosen to try and shock him out of it. Flirting heavily in front of several other girls on the way to kunoichi class Shika had hoped that the embarrassment would force Naruto to give up the ruse. Instead 'Ruka' as she called herself had just blushed and mumbled when he took her hand. Keiko had beaten him off at that point in a rare show of aggression, but not before he noticed that Naruto's henged hand felt exactly like a girl's. With his obsession with taijutsu it couldn't be natural, but the alternative that the dead-last had used to genjutsu to make him think he had small soft hands was ridiculous. The possibility that he'd actually temporarily turned himself into a girl was even more impossible, even if he did claim he'd invented a new jutsu…
Leaving the academy he stared at his hand, remembering the feel of Ruka's hand in his. Naruto did have stupid amounts of chakra. With enough chakra one could move mountains, create tsunamis, even fly. Orochimaru had reportedly gotten at least a quarter of the way to being a snake so was turning into a girl really that crazy? Yes, it was, but it still merited more research and surveillance. If nothing else Naruto's unusually good henge had given some more perspective on Keiko's pregnancy comment. Perhaps she had meant that Naruto was able to become pregnant, not that he actually was. Then again, if there was ever a boy stupid enough to become a girl and accidentally become pregnant without even knowing what sex was or how babies were made then Naruto was probably that boy.
Time, or exhaustive espionage, would tell.