As the story line develops, we learn that Shizuma has been persistently derelict in her duties as Etoile. She flees meetings and events where her presence as Etoile is required, with the result that the meetings fall into inter-school acrimony and the events are canceled or occur in a diminished way without her. Instead, she roams the campus constantly, either alone in the wilder parts of the grounds, or appearing suddenly and unexpectedly in the places Nagisa happens to be. Shizuma resists Miyuki’s appeals to fulfill her responsibilities, and is apparently indifferent to the consequences of her actions. She is determined to act as she pleases, and has closed herself off against any external influence.
Nagisa puts the question plainly to Tamao as to why Shizuma is acting this way. Neither understand what is going on, but we will find out later that Shizuma is acting partly out of despair since the death of her first love, and partly out of the wildness of her disposition, which refuses to be bound by others’ expectations and conventions.
In the "Attic" episode, we see Nagisa accomplish the impossible and return Shizuma to a function where her presence as Etoile is needed. Learning that there is to be a welcoming ceremony for the first-year students, and upset to think they might be disappointed if the Etoile does not attend, Nagisa refuses to accept Shizuma’s absence and resolves to go find her and bring her to the event.
The incident is a bright window upon Nagisa’s character. She is passionate in her indignation at Shizuma’s irresponsibility. She is impulsive, and sets off at once to look for Shizuma, forgetting even her trepidation at being alone with her in the urgency of bringing her back. She acts: where Tamao and her friends are inclined to passivity, she makes what she wants happen.
All of these passionate qualities are concentrated in the moment in which she confronts Shizuma, at the tree where they had first met. Nagisa actually grabs Shizuma by the hand to pull her back to the school, and then raises her voice to Shizuma in reproof and in appeal to come with her. When Shizuma ventures that she has been sent by Miyuki, Nagisa exclaims she "does not care what other people say," and insists she is acting for the first-years, and for their belief in and love of Shizuma herself. Then she is overcome by Shizuma’s gaze, and becomes faint as she always does whenever close to her, but even then she manages to clutch onto the arm of Shizuma’s dress to repeat her plea and pull her to her responsibilities. (The animation focuses on the intricate choreography of grasp and gesture; it would be worthwhile to do a moment-by-moment study of these gestures, to show how they signify Nagisa’s inner feelings.) Shizuma is amazed, and says to herself "This girl…"–and then consents, saying to Nagisa, "It’s your victory."
Why does Shizuma agree now, where she had been indiferent before? Clearly, Nagisa has impressed her with her passionate and active behavior. Nagisa does not defer to her: indeed, earlier in the episode we see Nagisa forget to curtsey to Shizuma when her companions do, and catch herself addresseing Shizuma by name instead as "Etoile-sama." Miyuki’s description of Nagisa as a "wind" is suggestive, comparing her to a natural force that has moved Shizuma. Shizuma’s response to Miyuki’s question, saying that it is her duties as Etoile that have brought her back, suggests complementarily that Nagisa has embodied the responsibilities of the Etoile. That, anyway, has been Nagisa’s purpose, whatever hidden motivations she might have to find Shizuma alone. By acting as Etoile, as Shizuma’s equal, Nagisa makes herself present to Shizuma in a new way, not as the latest girl in the sequence of monthly affairs, but as a true lover and companion-Etoile, someone to make up the loss of Kaori, the lost Etoile. When Shizuma says "This girl…" to herself, it is since she at this point sees Nagisa in this new light. It is from this moment their relationship really begins. We see them walk hand-in-hand into the reception, recreating the inaugural procession of Etoiles, and also acting as lovers, so that now Nagisa’s blush at Shizuma’s presence signifies attraction. If Nagisa in the end abandons the Etoile-election with Tamao, it may reflect the fact she has all along been the Etoile with Shizuma.
So the story of Strawberry Panic is that of a restoration, of Shizuma to herself, of the school as a whole to good order. Nagisa is the catalyst who makes all this happen. I am still wondering however what she receives, and how she develops, in the course of this narrative. Everything distinctive about her she possesses from the beginning. However, it may be that she simply perseveres, and maintains her passionate character in the face of ordinary life and disappointment. That by itself would be a signal accomplishment…