I sincerely doubt showing ayu's bare rear-end would be considered a liability, given her semi-sexual image at the time (and given what some male actors and singers have been doing in magazines at least over the last five years or so)... I know fans wanna keep the image of artists they like "pure" but... it's just a butt, being shown in a country where that's pretty much okay to show on tv
~ It's not like there's anything sexual about its depiction here.
That said, as I recall, I think she was too nervous to do it and it was a body double, but don't quote me on that.