Mahou Shoujo ni Akogarete

A team of three magical girls known as Tres Magia protects the town where Utena Hiiragi lives. Like many others, Utena loves these magical girls who valiantly fight in the name of justice. One day, a mysterious black mascot character appears before Utena and grants her the opportunity of a lifetime: a chance to transform into a magical girl. However, the offer is not what it seems, as Utena has been recruited for an evil organization to fight the magical girls she has always admired. Utena is then forced to confront Tres Magia in battle; but instead of feeling remorse, she unexpectedly finds pleasure in inflicting pain on the magical girls. Completely giving in to her desires, Utena embraces her role as a villain, slowly transforming her adoration for magical girls into a new sadistic obsession.