In other words, to date it was the one and only time that Shichika took on Nanami – so how did things play out?
Simply put, there was no winner.
Looking out for his sick sister, Shichika set a time limit for the fight – and within the allotted time, no winner was decided.
You could say that it was basically a draw.
None bore witness to the battle, but if any had – and were asked to make the call, whoever so tasked would have declared Nanami the victor.
The difference in ability between Shichika and Nanami was so great there was no contest.
The fight was not exactly undecided – she merely stopped before things went too far.
Like an adult humoring a child.
No – perhaps it was more like a puppy playing with its owner.
Nanami fielded every one of Shichika’s attacks – but never returned the favor, for the duration of the match.
Shichika expected his sister, up against him, to behave this way – but thought that if he pushed her hard enough, she would eventually fight back.
He thought wrong.
As it turned out, Shichika failed to get a rise out of Nanami. For nineteen years, he had been training without rest, through rain and wind and snow, but after all his effort, he was not even at a level where his sister felt the need to hit him back. Offense was out of the question, but she opted against even defense moves like the Ominaeshi.
Shichika, who based on looks alone seemed sure to win, wound up flat on the ground, which was as far as things went – ending the fight, the first they had engaged in their entire lives.
“You did pretty good,” Nanami told her little brother, when they were through. “Not as good as Dad was at his best, but you’re getting closer all the time. Keep it up – no slacking. Spare no effort.”
As one might imagine, Shichika was extremely sore about his loss – it took about a week for him to rally.
And why not.
After spending nearly every waking moment of the last nineteen years in training, he had failed to land a single swing against his sister, whom he had never seen practicing at anything, not even once.

Katanagatari Omnibus 2, Page 47