She was accompanying their family's Onmyoji in swordsmanship training.
Because Kamiyagawa's Wild Tachi Self-Manifestation Style had already broken through to Expert Level.
Now, he could attempt to comprehend and study the next stage of the Self-Manifestation Style's Silkworm Thread Strike—the Autumn Hair Slash.
"Divide time to a hairbreadth, like cutting the autumn fur."
He silently recited this advanced swordsmanship philosophy in his heart.
In this elucidation of philosophy, "hairbreadth" refers to the finest tip of autumn hair. As animal fur becomes extremely fine in autumn, the finest detail of anything is referred to as autumn hair.
This meant that swordsmen who employ the Tachi Technique, upon entering this realm, could perceive all the minute details of the battlefield.