Haruna: for me, Haruna is the one who brought SCANDAL's words and thoughts to fans to life, either in lives (along with Tomomi) or in MC's inside the live. Imho, she is the "bridge" between SCANDAL and their fans in said lives. Being a front-man/woman is really a big pressure and Haruna fulfilled that role really good imho. I think Rina thought about this too, which is why she kinda criticized Haruna's MC in one of their lives if you watch the NHK documentary thing. (Unless I understand that part wrong lol). The NHK documentary also summarized what happened to Haruna's voice and her determination to fix such issue. This determination is a good role model to some fans and inspire those fans in their life (among other motivations and inspirations of course). This would also show that SCANDAL isn't just admirable for their skills and talents only, but also their efforts in life and such.
Mami: I can't really say much about Mami. She really is that "mysterious" for me XD. But, from what little things I got, I think she's the one who the other members like to talk to whenever they have a problem. And of course (again, along with Tomomi) she's the one who can lighten up the mood.
Tomomi: Her cheerfulness. Imho that cheerfulness is something that could really lighten up the mood. And on a personal note, that cheerfulness of Tomo is one of the thing that makes me really interested in seeing various SCANDAL vids. It's interesting to think of what stuffs she'll do in said vids (sometimes, it's the little things that made it wonderful
). Her cheerfulness is also, what makes SCANDAL more... humane. It kinda reminds us that, despite being a famous group consisting of super cool and talented ladies, they are humans: enjoying and living the moment to the fullest. That is something I think fans can relate to, and can make fans like them even more.
Rina: She likes to keep in touch with her fans, from what I see. If Haruna is the one who connects SCANDAL and fans in lives, Rina is the one who connects them outside lives, especially through social media (blogs and tweets). I think this is a good thing and goes both ways: with Rina being sociable like that, fans could send their various opinions about SCANDAL (about lives, songs, etc). Those opinions could be something for SCANDAL to think about, so they could improve even further (haven't proven this myself though. This is just something I think could
happen. Or maybe it already happened.). And also, Rina could keep the fans updated on whatever events SCANDAL is attending/doing as said by Medios above. She is also the one who brought the "fan point of view" for SCANDAL (as said in a recent interview).
Welp, that's from me. Do remember it's just an opinion of mine, so forgive if it's a little illogical or something