Rosa is a vampire who waters 'white' roses with blood. Pretty much 'enough said'.
I think I'm the only person on the planet who liked the freaky blood-watering flower lady. She's nice enough, and can honestly send you flying with her battle skills. Why can't people respect that?

Her story in the game is quite touching... and I guess the way her humanity stayed with her, despite her evil-form inspired me to idolize her. That and she's killer with a longsword. Ouch.