The class that they had, the weapon wielding class where they were supposed to use their weapons and demonstrate various things, had ultimately turned into something like a direct guidance from their teacher.
After becoming distracted by Rain's sword, he did not want to leave the class on their own and wanted to see what the person who possessed such a weapon had in store for them.
So, he started a sparring session where he asked various students to go against him randomly.
It seemed random only to the others though, since the students could tell he was only asking those who were famous for their weapons and fighting styles.
Some were unexpected among them, some were unknown, but there were some who also had something unique about them– something that was only revealed when they fought against their teacher.
The competition was simple: they just had to land a hit on him and they would be the victors.