Joou ga Aishita Kaizoku

In sixteenth-century England, Lady Margaret was just eleven when her father died. He designated Christopher, a pirate, as her guardian, and decreed in his will that they were to marry. But Margaret, still young, was scared of Christopher, so he kept his distance. They lived a marriage in name only for years, which was never a problem for Margaret before. But now that she's eighteen, she desperately wants to consummate their marriage! Unfortunately, even though she's grown up, Christopher doesn't feel the same way... (Source: Renta!)