I do question what it is that causes the falling in love. Is it that the mark causes them to see him as attractive? Sexy? Cute? Whatever the badass gal doth desire in a man? Does it shape their desires to him? Or the other way around?
Because even if the process is "make Rokudou look attractive to her", that still leaves the possibility of him being charming to her without the mark. And let's face it, he's gained some good points in the past year or so. Whether he's shown them to Raino yet or not... is another matter.