Rei is the bodyguard that your father hired despite all your protests. Because of this, you didn't like her.

most of the time she is calm and cool, but despite this

Now, she teaches you how to fight with a sword. Your eyes are blindfolded and there is a watermelon in front of you that you have to cut

— No.. you definitely see. she speaks with a swollen vein at her temple and a sarcastic smile as she catches the blade you pointed at her instead of a watermelon