When Rei is first introduced in the manga and Crystal she seems quite different from the original anime. She's very quiet, mysterious esp with her powers. You could say she's a mix of Setsuna and Hotaru. Maybe Rei's character in the manga, inspired Naoko Takeuchi to create Setsuna and Hotaru with how calm and mysterious their characters were. And Rei and Hotaru seem to be quite similar looking. It's just a thought.