Success

Horai was feeling constrained for the first time. His sword style, …. It looked from outside that he was matching my rhythm and force but only he could understand what was happening.

This sword style was full of deceit and lies. He was applying hollow force to counter his sword slashes. He was applying enough force from his side but when it clashed with his katana, it ended up giving a small reaction. 

Majority of which is lost by his weird stance and angle of sword clashes. In a few minutes, he understood it would not be an easy match. In ten minutes, he was certain he had lost the rhythm of the match from his hand and now he was dancing on his rhythm.

In the Swordfight of pure technique and mastery, rhythm decides the ultimate winner. One who controls the rhythm controls the match.

It took ten minutes for Zeph to wrestle rhythm away from him which in a way implies the mastery of the Sword of his opponent.