She is a vampire, she can switch back for now to her male form because "he" was the strongest knight. It's the only vampire who can do this in the story, she is a very Very special case.
But everytime her vampires needs hit,she sleep or let her guard down and of course if she wants ,she will switch back to her real form, her vampire form.
The more she grow up as a vampire (She is just 1 year old) and the time passes , harder it will become for her to switch back to her male form and at a certain point impossible. It's explained by her "Vampire Mother" later. She also explains that nobody was able to do it before but that it didn't matter because she can't escape her fate that why her "Vampire Mother" let her escape. The Vampire Queen wants the MC to grow up, she cant really fight back against her needs and if she doesn't do anything about it she can go on a rampage etc.. So the MC is forced to act like a vampire no matter if she wants to.
Her brainwashing is pretty strong and only came back when she is in her real form even if she fights against it(for now) Her vampire form has a different personality and fight style... Kinda and she is way more clever than her male form( it's not hard her male form is stupid)
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