As a fan of time travel media, I say without reservation that this is the single best example in the 'genre'.
The film picks up a year after the end of the series. Kurisu and Mayuri are safe, and the Steins;Gate worldline has been reached. The Future Gadget Lab is inventing gadgets instead of time machines. The world is at peace, but Okabe is tormented by visions of the other worldlines, and he begins to slip away. At first, he only suffers headaches, but the visions get longer and more visceral, and he disappears entirely into another world line.
It is up to Makise to look for him, as she is the only one who remembers he is gone. The others have no idea. They are clueless. Daru is now the founder of the Future Gadget Lab. The world isn't radically different. Nothing falls apart. Makise gives lectures. Mayuri goes on Mayuri-ing. Daru hacks into CERN. Ruka practices swordmanship. A palpable sense of emptiness lingers over the lab, but that's it.
They still drink Dr. Pepper, though no one knows why. Okabe's influence is still there, but it is not attributed to him. As Bioshock Infinite posited, when the mind is confronted with a reality that its experiences can't support, it changes the nature of those experiences.
This is especially effective in this story, which is based around the concept of deja vu, which in Steins;Gate is a form of Reading Steiner. In the anime, Okabe was shocked to see that he was not the only one with memories of other worldlines. Ferris, Mayuri, Ruka, Daru, and Makise had these other worldlines imprinted on their minds, but they were regarded these memories as nonsense or dreams, just as we would. This is a lot like deja vu, and this film makes the connection even stronger. Deja vu is often foggy, like there's a fact floating out there in the abyss of your mind that you can't quite grasp, and in this film, the characters think of Okabe's existence in much the same fashion, like an ephemeral wisp that they've forgotten and can't quite remember.
Makise can remember better, but she has a hard time grasping his name, as though she is clutching at fog even as she is trying to return him to this worldline. She's the main character of this film, which just seems right. The last two episodes of the regular anime were about bringing her back, and the special was about bringing back the relationship between her and Okabe, so it makes sense for this film to be about her trying to preserve that relationship, to make sure it doesn't fade away. It's so natural, and it's a truly genius decision that helps this film stand out from the last two episodes and the special, that helps it stick in your memories.
She tries to go back in time and stop him from disappearing, but he doesn't want her to, not because he doesn't know what happen, but because he does know what'll happen. Her mind and soul will be torn apart as she desperately tries and fails to make things right. Her humanity will be all but gone, and she will be just a shell of a human being.
He knows this, as he has been through it himself, and he does not want to happen to her. In the middle of this film, he declares these thoughts in a speech to her, a speech that hits so hard, building off the conflict and dynamics that have been building from episode 1, pleading with her to not go back in time. Okabe delivers a lot of speeches at the end of the series and in the special about how hard it has been to time-leap over and over again. They all work, but this one is far above the rest, thanks to the writing, the context, and the amount of feelings and information communicated from Okabe to Makise. She didn't know what he was feeling before, but now she does, and it's torturous. She absorbs all of what he says because it's all completely true, and it's all so painful.
This film hinges on that relationship between Okabe and Makise in a way that no episode of the show, even episode 22, had, and it's wonderful. Their relationship is one of the most emotional, stimulating, and thoughtful in all of anime. I don't just care about these people. I'm enraptured by them, and the film deepens those emotions. It doesn't just capitalize on their relationship; it furthers it. The main conflict of the film is a conflict between them, which is fascinating and adds layering.
The love, care, empathy, and affection between these two people feels alive.
When the film ended, I was satisfied in a way I wasn't at any other point in the series. If the story of Okabe and Makise had ended after episode 24, or after the anime, or after the special, I would have felt content, but there would still be a piece of longing in my heart. There was no longing after finishing this film, except maybe the longing to watch it and the series again for the first time.
El Psy Kongroo.
