“Well, Nanami Yasuri – from what you’ve gathered, she’s a genius, and has immaculate eyes, right?”
“Y-Yes… Watch and Learn, they call it… There is no move or form that she can’t figure out if she sees it once, and master if she sees it twice – she sees it all. As much for swordplay as for ninpo… Most likely she knows every trick in the Bug Unit book by now.

Katanagatari Omnibus 3, Page 44