Starting on the 500th step, when Mira went in to attack the combat mannequin, she immediately noticed that there was no more rebound effect. Not only that, but when she tried taking off the head of the combat mannequin, she found it to be nearly impossible, which she found weird.
Usually, she would be able to remove the head with little to no effort but now things seem to have changed. Mira then tried to remove the 'heart' of the combat mannequin, but quickly found out that she was unable to penetrate the mannequin.
Even though she hadn't used her full power to attack, she did use around 40% of her power. Just with that knowledge and with how her attack felt while hitting the mannequin, Mira knew with absolute certainty that even if she used her full-powered attacks, she wouldn't be able to damage the mannequin.
