Yuki turned, her eyes falling upon the fully-formed wearer of the blue sling bikini and immediately fell in love with her. Buffy was just so incredibly hot! How could Yuki deny being with someone like that? What exactly was she doing anyway? Trying to escape? Why would she do that? Everything she ever wanted was standing right in front of her.
And as she stood there, the last of what made her female disappeared. Her new penis grew long and hard at the sight of Buffy's magnificent curves and femininity, as she became completely male. And thus, Duke was born.