Da-in Yoo
Yoo da-in is the protagonist of the manga and at the start he is a really "pretty" guy so he was often mistaken for a girl. Shortly into the manga he is changed into a vampire and turns into a girl! (In the English version, they renamed 'Yoo Da-In' to 'Gene Young' and 'Yoo Da-Young' to 'Jean Young.')
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Mangaography