Yuu was disappointing? You didn't think it was awesome that she burns words into the ground with her magic, that she can command others to die, and that her magic is strong enough that it negates attacks (like a hotter fire engulfing a weaker one)? It made it quite clear why she slapped Haruna earlier. The simplest words hold immense power when Yuu speaks them. I've always liked the premise that words themselves have a kind of power, and she fits that rather well.

Ayumu delivering the beatdown was nicely delivered too. He stole her magic, then went after her spare lives. You could hear her screaming just slightly over the background music, leaving exactly he was doing to her up to our imaginations. It ended nicely with Ayumu remaining loyal to Yuu by not taking her final life, knowing that she would be the most disappointed if he didn't treat life with the same respect that she does.

As for the teacher, it was surprising that she is that much more powerful than her students. She probably isn't that far off from Yuu's strength.