Keiko Kubo

Here's an Amazon description of Keiko's 2003 movie Kekko Kamen.

A beautiful young girl named Mayumi joins a top-notch announcer school with draconian disciplinary standards. Because she had spent her childhood abroad, Mayumi soon falls behind her classmates. Though subjected to merciless flayings by her teachers, she continues in her quest to become an anchor Woman. While being beaten by especially cruel teacher, strapped to a rocking horse clad only in her underwear a woman appears identifying herself as the "Kekko Kamen", completely naked except for a red mask covering her face, , she stands up to defend the tormented Mayumi and battle the sadists of Manglifon school.