The decisive factor is Kaori’s letter, which Miyuki finds tucked away in the box for the Etoiles’ pendants. Kaori had foreseen that her death might devastate Shizuma. So she writes Shizuma a letter, which she intends for her to read after she dies, to forestall that unhappy outcome. In the letter, Kaori tells Shizuma to live after her death, to go on out into the world outside of their school, to keep close to her friends, and to have new relationships. Above all, she tells Shizuma to remain herself, the person whom she loves: "Shizuma, be free. Stay the way that I love you, the beautiful, strong, capable, and free Shizuma. Forever and ever. Please, Shizuma. Kaori."
Up till now, Shizuma had resisted all inducements to change that came from the outside, whether from Nagisa or Miyuki, for the sake of Kaori, whom she holds within herself. But to Kaori herself, who speaks to her from inside the fortress of her heart, Shizuma can have no such barrier. And so she listens at last to a plea to get over the loss of her love. Precisely since Shizuma still loves Kaori, since fulfilling the terms of her letter is a way of connecting one last time to Kaori, she takes Kaori’s letter immediately to heart. Shizuma’s first reaction is to connect Miyuki with Kaori’s advice "[t]here should be some one beside you who is always supporting you," and to acknowledge to Miyuki her special role in her life: "You’re my friend…my only friend. I couldn’t go on without you. I…need you." Miyuki is overcome, and embraces her. Already Shizuma has stepped out of her solitude, to appreciate the role Miyuki plays in her life, and to recognize that she herself is not self-sufficient, that she needs other people. In a nice antithesis to their previous conversation in the episode, where Shizuma had insisted she and Miyuki were fundamentally set apart from each other given that Miyuki had never shared Shizuma’s experience of love, now Shizuma recognizes a deeper connection between them based on friendship, of shared support and need. As Nagisa does in the previous episode, Shizuma begins her emotional recovery by integrating herself back into a social network of friendship.
A measure of the distance Shizuma has traversed is the fact that she now encourages Amane to become Etoile and to move forward her relationship with Hikari. Again, the anime provides a neat antithesis to Shizuma’s attitude of the day before. Then, to Amane’s question as to what the position of Etoile meant to her, Shizuma had disparaged the job as so many tiresome responsibilities. Even its personal aspect, the relationship between herself and Kaori, however transcendently significant–"[f]or certain, at that time…[w]e…had attained something…words could not describe"–she considered to be finally evanescent, a condition of loss. In a brilliant piece of animation, the anime indicates this idea visually, by showing us Shizuma after saying these words looking down at her empty hands. Now, however, she urges Amane to become Etoile, for the sake of the relationship with Hikari: "[y]ou have to become Etoile and attain something that only the Etoile can get." "And what is that?" ‘Find it yourself. It’s not something you can get alone." To make it clear that Shizuma is referring to Hikari, the animation pans over and centers upon Hikari singing in the choir behind them. Shizuma now understands the real value of her time as Etoile with Kaori, seeing it as something precious, and worth Amane and Hikari’s finding for themselves. She understands the position to exemplify that aspect of life one does with someone else, that cannot be realized by a single person. And finally, she understands the deep message about love that Kaori is exemplifying by her letter: that love is best expressed by extending to others, that just as Kaori seeks to bring Shizuma forward to new love, so too should Shizuma bring others to love.
Shizuma brings her fulfillment of Kaori’s letter to its culmination at the climax of the episode, when she returns the Etoiles’ pendants to the cathedral. Given that the pendants are to her emblems of the life she shared with Kaori, we can understand her act to return the pendants also as an intentional turning of Kaori’s page in her life, to go forward to a future without her. In confirmation of this decisive psychological step, just after she has set the pendants’ case down, Shizuma whispers "goodbye" to Kaori, and hears Kaori respond "goodbye" in return, while her image rises upward toward heaven and disappears. The anime provides us unambiguous evidence that Shizuma has at last released Kaori from her heart, and has become reconciled to her death. Kaori’s part in Strawberry Panic is now over.
There is no doubt Kaori’s letter acts as a deus-ex-machina in the plot, to move the narrative past the block Shizuma’s prior relationship with Kaori represented. In apology for this literary device, I repeat the point made above, that it is logically consistent with Shizuma’s characterization to this point, that she has sealed her heart against the outside, and can only be moved from within, by Kaori herself. Also, we can argue that the letter answers to steps in the same direction that Shizuma had made before getting the letter. I am thinking of how she tells Miyuki that she is sorry for hurting her, how she reflects to herself that she is always hurting others, especially Nagisa and Miyuki, and then how she decides–to Miyuki’s surprise–to attend Miyuki when she does to fetch the pendants from Kaori’s old room. If we link these scenes, we can understand them as to signify regret followed by an effort of renewed responsibility, whereby Shizuma on her own moves in the direction the letter will take her. If the letter is a deus-ex-machina, it enters a scene that Shizuma has already morally and psychologically prepared.
Finally, Kaori’s gesture maintains a pattern we see repeated throughout the series, whereby the third girl out deliberately and dramatically delivers her beloved to her rival. This moment occurs in all of the significant relationships narrated in Strawberry Panic: Miyuki helps Kaori walk over to Shizuma at the Etoiles’ inaugural ball, Yaya urges Hikari to go to Amane after the duel with Kaname, Kaname gives up her secret attraction for Amane and convinces her through the duel to stand for election as Etoile with Hikari, and, most spectacularly, Tamao pushes Nagisa toward Shizuma at the series’ conclusion. That Kaori does not go quite so far, to deliver Shizuma into Nagisa’s hand, is due to the circumstance of her death, which closes the specifics of the future from her sight; but so far as she can, Kaori means to separate Shizuma from her, and to hand her over to her future, and her future lovers. So Kaori’s letter does not enter the narrative anamolously or artificially: rather, it confirms a pattern in which all rivals lay down their contention, and celebrate the destined lovers’ union. In Strawberry Panic, love includes both lovers and friends: complementing the union of the two beloveds is the reconciliation of all rival friends to their love. Love conquers all.
In closing, I note the paradox by which Kaori bids Shizuma to be free, and Shizuma dutifully fulfills her instructions. Is this freedom, or is it Kaori’s shadow under another color? Certainly Kaori sets out an ideal of Shizuma, but which is also an understanding of her character, seen in its best light, from the perspective of one who loves her for her own sake: "[s]tay the way that I love you, the beautiful, strong, capable, and free Shizuma." If Shizuma simply repeats the letter, for Kaori’s sake, then she has not really achieved what Kaori asks. It is up to Shizuma to act and to live on her own the terms of this ideal, to give them their specific meaning in the particular events of her life. Shizuma’s steps in this episode are only a beginning, insofar as she is acting under Kaori’s influence: that is why the series is not over, and why the relationship between Shizuma and Nagisa does not go directly to its conclusion. She still has to learn to be free. The remainder of the anime amounts to a waiting for Shizuma herself to get up, to act for herself, to be free on her own account.
Appendix: the text of Kaori’s letter in full:
"To Shizuma. You’ll read this letter someday. When you do, I wonder how you’ll feel? Right now I have no regrets. *Just that I pray that someday this letter will reach you. **Do you remember? The days after we became Etoile? *Under the guidance of the past Etoile, the first time we entered the greenhouse. I fell in love the first time I saw it. The greenhouse is very pretty. No matter what season it is, there will always be the sweet scent of flowers and plants. Cold winds and rain don’t reach there. Just like the place we live, Astraea’s Hill. Hey, Shizuma. I’ll disappear before I’m able to see the outside world. To be protected by your warm love, and seeing the rain pouring down of the outside, I feel very happy. I have never once thought of leaving this place. I love it here. But Shizuma, you are different. You can walk under that cold, windy rain and look at the new world. There should be some one beside you who is always supporting you. And…look ahead. A brand new world awaits out there. You will surely have new encounters. Shizuma, I love you. Shizuma, be free. Stay the way that I love you, the beautiful, strong, capable, and free Shizuma. Forever and ever. Please, Shizuma. Kaori."
*narrator’s voice switches to Kaori. **Kaori and Shizuma speaking together. The narration opens with Shizuma’s voice.