Vivy once again saves Kakitani along with a handful of Toak operatives, but Kakitani is once again ungrateful and Matsumoto determines it will be hard to conceal the fact that the AIs of Metal Float killed a fair number of humans, all thanks to Dr. Saeki’s apparent “shutdown” program caused all of the AIs to rampage, like antibodies fighting off an infection.
Saeki’s personal stake is put into context as we learn he was once a patient at the facility where he’d eventually work. As a child, it fell to the nursing AI Grace, descendant and Sister of Diva, to tell him his parents abandoned him, and to comfort him.
When he returned as a researcher, he fell in love and proposed to Grace, and they became the first official human-AI couple, with Grace considering marriage to be a logical step in her attempt to better understand humans as part of her mission to save and protect human lives.
When Vivy confronts him, he reveals his true plan, which at first he believed aligned with her and Matsumoto’s goals: like them he intended to shut down Metal Float, but he also intended to retrieve the data comprising the “soul” of the real Grace, who had been forcefully appointed the island’s control AI, and her mission rewritten.
Saeki tries to prove to Vivy that the Grace he knew and loved is still imprisoned in the core, singing Diva’s song (and incidentally, the opening theme) on a loop as a kind of distress call. But both she and Matsumoto hear the “singing” for what it is, nothing more than “tone data”. The Grace Saeki had hoped to download into his replica Grace no longer exists.
After Vivy makes clear to Saeki that in her current form she is not Diva, but Vivy, “an AI who will destroy AIs to change the destructive future”, he siccs his Grace replacement on her, but she’s able to easily defeat her thanks to her combat program. Matsumoto then determines the best place to look for the Grace core is the island’s main tower.
He proceeds to hack the production facility to quickly manufacture dozens of Matsumoto cubes, which coalesce into a kind of flying mecha Vivy uses to fight her way through the waves of defense AIs to reach the tower. Trippy Tron-y baroque neon spectacle set to the theme song ensues, to the point it’s hard to tell what’s going on at times, but it’s definitely cool-looking.
Vivy’s final obstacle is M205, who attempts one last surprise to detonate in her proximity in order to neutralize her, but Matsumoto mecha shields her from the explosion. While her face is damaged, Vivy enters Combat Mode and puts her arm through Grace’s chest. The island shuts down, making the operation a success. But it’s also framed as a death of honor and mercy, freeing Grace from a mission she never wanted.
But this success has immediate consequences. Despite Vivy’s hope and desire that Saeki be able to find happiness elsewhere in the wake of the loss of his love, Saeki instead chooses suicide by putting a bullet in his head, thus joining his lost love. As a result, in this instance, Diva failed in her mission to make people happy with her singing.
With one hand drenched in Saeki’s red human blood and the other in Grace’s blue AI blood, Vivy has a bit of an existential crisis. While Grace accepted the mission rewrite and assumed her new role as control AI of Metal Float, Diva/Vivy has maintained all along that her mission has not changed.
But one cannot deny that she’s suffered quite a bit of mission creep, and the resulting complications in her new dual role as savior of humanity is having a deleterious effect on her sense of being, and possibly her very sanity. We’ll see how this carries over into her next operation, whenever in the future that might be. But I imagine her condition will continue to worsen before it improves.