Nanami Yasuri.
But the power of her vision went beyond acquiring the moves of others – nothing could get by her.
No trick, no motion.
No weakness.
Seeing through it all, without exception – Nanami Yasuri watched and learned!
“...then!”
Of course Shichika knew.
He’d spent most of his life beside his sister, and her eyes were a fact of life. Not even twenty-four feints sufficed – she must have seen every last one of his feints for the fake it was.
And that was only the beginning.
His sister knew everything about him.
She knew every move the Kyotoryu had – and knew them better than anybody in the history of the school. Ths ins and outs. The pros and cons.

Katanagatari Omnibus 3, Page 16