When you're being attacked by someone, you've got three options. You can let them hit you, or you can defend against the attack, you can evade the attack, and finally, you can clash. We'll get into those later.
Right now, I can take the damage, and let her attack hit me.
Stamina: 500 - 100 = 400
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You must note the loss of Stamina, immediately after you are hit.