On the topic of anime girls added via adaptation¹, I really like the essay "Nanami, Anthy, and Escaping the Script" by Giovanna @ Empty Movement.

 The birth of Nanami Kiryuu was not planned by Be-Papas. The manga version of Utena, which was produced concurrently with the television series, doesn't include her beyond a photograph, and the movie that followed excludes her with an equally irrelevant cameo. Though she appears in other iterations like the musicals, game, and novels, it's safe to say the manga, series, and movie are our holy trinity, and Nanami is only prominently depicted in one of them.

 This prominence is the work of a single screenwriter: Noboru Higa. Rumoured to be Ikuhara himself under a pen-name, Higa reports having instead met Ikuhara at a veterinary hospital. This may or may not be true. What we do know is that Noboru Higa is a pseudonym used only for the production of Utena¹ by writer Ryota Yamaguchi, [...]

    So what scripts did they order from this screenwriter, then? Noboru Higa wrote Nanami episodes. Only Nanami episodes. ALL the Nanami episodes. He is not, however, a member of Be-Papas, and Nanami was not part of the original conception of Ohtori Academy and what would happen within it. She’s given a unique place within the story, both part of it and not, and though she seems meant to help explore and illustrate the central themes of Utena, she ends up having a mind of her own, and in a very real sense, deviates from the script.

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1. Yes, I know the Utena manga and anime's relationship is more complicated than "the anime is an adaptation of the manga." I think the fact that she wasn't created by Be-Papas still places her in a similar category as Meiling Li in Cardcaptor Sakura, Nosaka Miho in Yu-Gi-Oh!, and Makibi Kiyone in Tenchi Muyo of "adaptation-exclusive major female character."