We have all been, or are, a fan of someone
When I was a teenager, my class was roughly divided into several groups (factions): Johnny's (mainly Arashi), AKB48, among others. Whenever we went to karaoke, idol songs were always sung. I liked Western music, but I was somewhat embarrassed to be singing only English songs in front of my friends, so I listened to Arashi and AKB48 songs as well, just in case. I wasn't really interested in idols at the time, but I knew I had to at least know them to have fun with my friends. To my surprise, three years ago I became an idol fan myself.