When Cleo goes into a fit after seeing Zess go down against Rygart. She takes him out in just two kicks and holds off a squad of Golems by herself while a squad mate gets Zess out of there.
Girge destroying ten elite golems. By himself. while his golem had a missing foot.
Lygartt destroying most of the enemy army single-handedly in chapter 51.
Chapter 67. Just... chapter 67. Rygart VS Zess. Rygart completely and utterly OWNS Zess, to the point that Zess had to wonder "Who exactly ARE you?"
Cleo follows up after Rygart's aforementioned moment with Ch. 70 when she and her familybust Sigyn out of prison, becoming traitors to Athens in the process. If there was any doubt that Cleo had matured from the ditzy girl who barely knew what to do in a fight that she was at the start of the series, this dispels all of it.