Okay this is my favourite scene ever. Because Usagi did never react to Endymion since Beryl’s words, because she was so scared about hurting him that she preferred to be passive… But look at this. Look at her eyes the exact moment she realizes that, if she doesn’t do anything, her friends will have been died in vain. Look at her hand. There is a devastating anger, a crushing rage, the images of her dead friends are still before her eyes and she just can’t let this happen. She understands the beauty of their sacrifices, she gets to see the price of her passiveness and she chooses not to accept it anymore. She hits the man she loves more than anything because she finally understands, she lets this fire catching.
This is the only time we get to see Usagi this angry, trembling, vibrating. There is no sadness anymore. Just an ancient fury. This is the moment she deeply understands Rei’s slap. This is the moment she chooses to fight, as her friends did.
In this small, exact, ultimate second, we see at last Usagi truly becoming Sailormoon.