After watching Utena, I've thought of Anthy as an irrelevant, weak character, as she hardly seemed to accomplish anything on her own. However, as I thought it over, I figured that she was far deeper than she seemed to be at first.
The main reason for my outlook was, as the title indicated, her passive-agression. Though one may not notice it the first time around, Anthy uses roundabout tricks as a means to seduce Mickey and Juri into fighting against Utena and, thereby, playing a part in her brother's masterplan.
She does this by playing at the characters weaknesses: namely, their love interests. She does a certain activity which the love interests are known for in order to form a connection between herself and said love interests, hence making herself the object of affection for these two who cannot get gratification from their original objects of affection.
With Juri, this is her friend, whom she cannot confess due to it being a lesbian predilection. Her friend is shown to have an interest in men. She is also shown to offer Juri an orange flower (a rose, I suppose, in keeping with the general symbolism), an action that Anthy repeats to Juri in the episode focusing on the latter. Juri slaps her off her feet, as she probably understands the reasoning for this and is angered by it. The same action is repeated by Anthy once Juri loses to Utena.
Mickey is easier to trick, however, and doesn't see through Anthy's deception. His love is for his own sister, obviously a taboo, and manifests itself through the symbol of the piano, as it is through the piano that the two bond, over the piano that two break up, and through the piano that Anthy seduces her. If you notice in the first episode to focus on Mickey, he visits Anthy due to the belief that he has fallen in love with her. By the end of his visit, he seems to be disillusioned somewhat with said love until Anthy reinstates it by playing the very same piece on the piano that Mickey and her sister were accustomed to. This reinvigorates him in his pursuit. (of course, touga has to have sex with his sister and go homo on him for the final push but that's neither here nor there)
I can't remember an instance where the other contestants were affected in such a way, so do comment any examples that may come to your mind.
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