20-year-old pop star Minami Minegishi tearfully apologized to her fans with her head shaved as an act of contrition.
"Everything I did is entirely my fault, I am so sorry", she told her fans in the tearful video.
Her mistake, she says, was "spending the night" with a singer from a popular boy band.
Minegishi has been demoted within the Japanese supergroup AKB48.
While girls are not banned from dating, they are encouraged to maintain an image of innocence and purity for their fans.
But critics say the group's videos are anything but conservative - showing young girls in very skimpy outfits.
The fans chose who the superstars will be, voting for their favorites, after buying a cd of course.
It's a music democracy that is minting money, and again generating controversy.