Truely, the only one for me was my brother..he was the only one I had..
Kiryuu Nanami appears to be something of a bully in Ohtori Academy.  She knows exactly how powerful and popular her older brother is and uses it to her advantage.  Several girls flock to her as friends, the three closest of them became her bully girls.  Nanami seems to be proud that she's used her position quite well, something her brother would be proud of. 
There seems to be a great deal of confusion when it comes to Nanami, as to where she stands with her brother. Some misconstrue her adoring attention as misplaced love, when in fact, this is not the case. However, one would not be able to tell if one had not seen beyond the first 13 episodes.

Nanami's role often calls for humor, in her dastardly attempts to spoil others, the joke usually ends up on her.  Touga seems to have gotten used to this sort of behavior, and regards it with minor annoyance.
Nanami's first duel with Utena was agitated by Touga, who had not been quite ready to take on the Victor just yet. Nanami, having been thrust into the game without knowing the rules, played at her own pace.  However, she lost anyway, and in doing so fell into a rage that nearly killed Utena and herself.  Even after the incident, Nanami stayed in the dueling game, and Utena and Nanami became good aquaintances, but never quite friends.

Nanami's move to stay with the Student Council was a wise one, because as soon as her brother had lost the duel with Utena, he vanished from campus life all together.  And with no acting president, the council would fall into ruin.
Nanami takes over all of Touga's duties while he refuses public life.  She bears up quite admirably, even when Miki and Juri only humor her.  Nanami continues with her pranks, as it is her nature to.  Mitsuru still does her bidding, as do her lackey girls.

Nanami is often given to radical ideas as to how she fits in with the others at Ohtori Academy.  In ne episode, she parades around in a cowbell she mistakes for a very fashionable necklace.  Utena seems to be the only one to tell her that the cowbell is for cows, not people.  Either everyone else is too busy laughing behind Nanami's back to say anything, or too timid to say anything to her face.

And while Nanami may try to exhibit nothing but a strong facade in front of her peers, Nanami is actually very self concious and worries about how others see her.  Her main insecurity seems to come from her brother's 'lack of affection' toward her. This may be so, after all, he is a few years older than her, and no longer behaves like a little boy.

To further that insecurity, Touga further prods it, suggesting that he and Nanami may not be related at all, which isn't true.  Touga seems not to care too much for anyone other than Akio and Utena by this point, and Nanami takes it upon herself to leave the Kiryuu house and pursue dorm life, living with Utena and Anthy in the Rose Tower.
However, Nanami's stay in the Rose Tower is short lived, and Nanami herself succombs to Akio's manipulation, and duels once again, this time with her brother as her bride.

Even with Akio's urging, Nanami is unable to overcome Utena's blade.  She moves back in with her brother, having dispised Anthy and Akio so much for what she'd seen.  Utena's influence seems to have even reached Nanami, and she also attends the vigil and final meeting of the Student Council.  And since she had not been in it from the beginning, she didn't feel the need to keep her ring until the end, as the others had.

Would Nanami forget Utena, as many others had?  Perhaps. Afterall, Touga did prefer Utena over any of the girls, and that in the past would've been enough for Nanami to hate her. But Utena taught Nanami modesty. Perhaps....she had not forgotten the name Tenjou Utena after all.
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