[Her dad kept her in the basement because of bad people. Her existence was completely unknown prior to her returning to her pureblood state about a year and a half ago. That was how a pureblood vampire could just go missing without anyone blinking an eye. They didn't even know she was alive as they kept her in a basement.
Zero is massively conflicted by this news. On one hand, human children were high on the desirable list. A pureblood child--well--Zero was hungry and it was hard enough being around Yuuki when she was older. Being a child was just making it worse. On the other hand--locked in a basement without sunshine was practically a crime for someone like Yuuki.]