I heard Koda's fans are mostly girls and gay guys 
Don't know about the gay guy part, but the girl part's definitely right.
The girls here just idolize her, and copy her hairstyle like they did a few years ago with Ayumi and Namie. And seriously, it's damn hard to find a girl 15~25 who isn't a fan.
My source: Well, I teach at an all girl private senior High School ( 900 girls aged 15~18 ), and music is one of the main topics of conversation.