When Diva’s code degraded into oblivion and Vivy re-awakened and took her place on the stage, Diva’s final song was already over. Ever since then, Vivy has been unable to sing, still unable to find the answer of what it means to “sing from the heart”.
So she retired to much fanfare and took up residence as an exhibit at the AI Museum. Decades passed, and humans and their children gradually forgot about her and her contributions. But not all: Osamu, a young lad on a field trip, knows full well who Diva was, and is.
Osamu wants to hear Diva sing live, but she tells him that’s not possible. When Matsumoto shows up after a good number of years, Vivy is eager for their next mission together, as it’s not “all she has.” But Matsumoto tells her the Singularity Project is over; the double suicide of Ophelia and Antonio didn’t lead to any copycat incidents; a positive revision to the timeline.
Yet despite the fact they’ve seemingly achieved victory it preventing the AI uprising, something Kakitani said still haunts Matsumoto: “through a revelation from the heavens.” That led him to meet Vivy now, sixty-five years from when they first met. He proposes a “race”: whoever finds their answer first wins.
Vivy goes into the archive and dredges up her first memory, when her creator (a female researcher) gave her her mission to sing from the heart, hoping it would “offer a hint” as to what a heart is, at least as it applies to humans.
Osamu visits Diva again, saying it’s “messed up” his classmates don’t know her. Inspired by Matsumoto, she proposes a race, with him bringing friends to meet her while she searches for the answer her creator knew full well she might struggle with her entire life.
As one year, then five, then ten, then twenty pass by, Vivy writes a song in the Archive, which if completed would be the first instance of a song written by an AI of their own pure free will (all previous songs were written by humans). Her progress is glacial; unable to come up with more than a couple of phrases and constantly erasing notes she’s put down.
Meanwhile, Osamu has quite a bit more progress in those years, making friends, making a career for himself in research, and eventually meeting and marrying his wife Nana. While Osamu and Nana are able to conceive, she dies of an illness shortly after giving birth, leaving Osamu both a father and a widower.
He visits Diva with his daughter Luna in his arms, and asks if she would like to hold her. Diva asks why Nana was able to smile despite knowing she wouldn’t live to see her daughter grow up. Osamu tells her that all humans die, but they always remain inside someone or many people without fail. Such is the case for him with Nana and, as Vivy realizes, it’s true of her and Diva as well. As little Luna grasps her hand, Vivy is hit by a sudden spark of inspiration.
She dives into the construct and belts out a completed song, written about her and Matsumoto’s journey in the Singularity Project, and of all the people she’s met. When an impressed Matsumoto shows up and asks who she wrote it for, Vivy says it’s for Diva, who remains inside her even though she’s gone.
After twenty years, she was finally able to finish her task…yet she still cannot even contemplate singing it, so her struggle continues. Before that, though, Vivy goes into hibernation mode, resting her circuits after accomplishing her singular feat.
Her friend Osamu, who along with his wife and daughter inspired Vivy to do what no other AI has, can see that his friend Diva is in deep sleep crunching music data. He leaves her to her creative slumber, assured that when she wakes up he’ll finally be able to hear her voice. Then someone off-camera calls Osamu by his last name…Matsumoto.
Unfortunately, the joy that comes with the revelation Vivy’s cubic partner was a friend and admirer from her future all along is soon overshadowed when Vivy wakes up to find the museum in burning ruins. She runs outside, where the AI apocalypse is in full swing, with one key, horrifying, heartbreaking new wrinkle: as they murder every human in sight, all of the AIs are singing in sinister, dissonant unison. They’re singing Vivy’s song.