I think I picked her originally based on looks; but everything I have learned about her has made her stand out from the other girls. True, she is not the most talented of her group, on what singing matters pertain, that's Hinako's distinction; but she's a very hard worker. She has improved so much over the years through practicing hard.
She is the leader of her team, and the rest of the girls appreciate and admire her. Well, at least Kaede does. She also work in synergy with the backing band's leader; together they make "Team PassCode" work.
She's the most social of the girls. If she doesn't "make contact" with the band members they share stages with, they'll probably won't at all, unless the "others" come to interact.
Yes, my ultimate bias is Japanese, not Korean, and is not a member of a "cutesy" jpop group; she's a member of an alt-idol group playing loud rock.
But she, Nao Minami, is my ULTIMATE BIAS. Enough said.