In the year 2161, on an Earth where Artificial Intelligences have long lived alongside humanity, the NiaLand amusement park has descended into chaos and bloodshed as A.I.s rampage through the streets and attractions with smiles on their faces, ruthlessly murdering any humans they come across. Not just NiaLand, but the entire world has been overtaken by a massive A.I. rebellion at precisely the same moment, and within minutes, ten-thousand humans are dead. Determined to avert this terrible future, an aging A.I. researcher enacts a desperate plan, using a time machine in his final moments to send data one hundred years into the past within the code of the world's first fully autonomous A.I., a musical robot named "Diva" whose original mission is "to make everyone happy by singing".
In the year 2061, Diva ends her latest performance on a small stage at NiaLand to an audience of three, then goes backstage to talk with her only human friend, a young girl named Momoka, who after their first meeting christened the songstress "Vivy" after a picture-book character she resembles. Giving the A.I. an early birthday present in the form of a high-tech stuffed bear, Momoka secures a promise from Vivy that she will one day sing on NiaLand's Main Stage. Her friend departing, Vivy steps back onto the stage to sing to an empty audience... and then packets of data from the future hit her.
Taking on the name of his developer, "Matsumoto", the A.I. program from the future inhabits Vivy's new stuffed bear and, in spite of her protests, enlists her in "the Singularity Project", his mission to covertly change history and avert the coming war between humans and A.I.s, a mission she is dragged into whether she likes it or not.
Vivy: Fluorite Eye's Song provides examples of:
- 2D Visuals, 3D Effects: Matsumoto in cube mode is rendered in 3D animation, as are the vehicles and most other robots.
- 20 Minutes into the Future: Although the main part of the story ostensibly starts only 40 years from now, technologies like robotics and artificial intelligence are incredibly advanced by modern standards, and only get more impressive as time goes on.
- A.I. Is a Crapshoot: If the worldwide A.I. rebellion in 2161 is anything to go by, this trope is definitely in effect.
- Broken Record:At a certain frequency, Dr. Saeki was able to intercept Grace (now Metal Float's AI) singing 'Sing My Pleasure' on a repeated loop which he interpreted as her cry for help for him to save her but Diva/Vivy concluded that it was tone data that was not wiped out when she was reprogrammed and the Grace he loved was gone for good. However, the writers Twitter post on the episode wrote whether or not Grace was still 'alive' was left ambiguous.
- Bad Future: The original timeline's year 2161, when A.I.s across the world rose up to destroy humanity.
- Call-Forward: In the opening scene set in 2161, almost all the clothing seen consists of white, gray and black clothing decorated with lime green luminescent lines. When Matsumoto jumps back into the past, the fashion borders on No New Fashions in the Future. In Episode 7, which is set around 2121 after a forty-year Time Skip from Episode 6, various characters are a seen wearing clothing decorated with lime green luminescent lines reminiscent of those seen in 2161.
- Colony Drop: The plot of the second arc revolves around preventing the Sunrise Hotel from doing one of these. In Episode 12, the Archive subjects all of Earth to this by dropping thousands of satellites onto major cities.
- Diegetic Soundtrack Usage: The ending theme, a calm piano piece, makes an appearance in the series itself in episode 10. It is the song composed by Vivy herself over the span of a year, the song she put her feelings about the Singularity Project into, and it can be heard being hummed creepily by the rebelling A.I. in the post-credits scene.
- Don't Create a Martyr: Vivy's first mission boils down to this. In Matsumoto's timeline, the murder of an assemblyman in favor of passing an AI Naming Law motivated politicians who were also in its favor to put much more effort into getting it passed in his honor. The law doesn't get passed in the timeline in which he stays alive, but an even more favorable law gets passed instead.
- For Want of a Nail: When the central plot is about changing history to avert a Bad Future, this is bound to happen. Perhaps the most prominent is the Ripple Effect of a different Sunrise Hotel incident where, due to Estella's Heroic Sacrifice, human-AI relations were not badly affected and actually improved but this came at the cost of Dr. Saeki and Grace's marriage since human-AI relations were never jeopardized in the new timeline, and Grace was converted to run Metal Float, a project that was supposed to come online later but was accelerated instead, before Saeki could propose to her, and ended up hurting humans, putting a crimp in human-AI relations.
- Grandfather Paradox: It turns out that Vivy's impulse to save Yugo Kakitani during her first few missions was intended to avoid one. Osamu Matsumoto's creator's higher-up in the Toak moderate branch is Yugo Kakitani's granddaughter.
- Grow Beyond Their Programming: Even though there's a rule that each A.I. can only have one mission, fully autonomous A.I. like Vivy/Diva and her successor series A.I., the Sisters, seem to do this constantly by twisting the definitions of their missions. For example, Matsumoto persuades Vivy to take part in the Singularity Project not by taking her current audience members into account, but by considering that the lives of future, yet to be born audience members will be lost and that if she does not act, she won't be able to "make everyone happy by singing".
- Heroic Sacrifice: The ending of the Sunrise Hotel arc, in which Estella and a reconfigured Elizabeth stay on the Sunrise after evacuating everyone else on board to ensure that it breaks up and burns in the atmosphere. While in the original timeline Estella was known as the most defective AI in history, in the new timeline she's seen as a hero.
- In Spite of a Nail: Even with all the differences in key points of AI evolution and how society reacted to those points, the Robot War still happens.
- Nice Job Breaking It, Hero!: In the first arc, Matsumoto hopes to prevent the passing of the AI Naming Law, a law that would grant A.I.s human rights, by preventing the murder of the assemblyman whose death would rouse the other assemblymen into passing the law in his honor. The assemblyman himself even admits he couldn't care less about AI and only wanted to pass the law to gain votes. While his survival does prevent the AI Naming Law from being passed, Diva inadvertently inspires him to pass a stronger law that is even more favorable for A.I.s.
- One Steve Limit: Averted. Things start getting awkward when Matsumoto meets with the new timeline's version of his creator and he insists upon being the one called by their inevitably shared name.
- Painting the Medium: Scenes from Matsumoto's timeline are depicted with letterboxing. When a scene begins to diverge from that timeline, the letterboxing disappears.
- Another instance happened in Episode 6. When showing Saeki's flashback to how he fell in love with Grace and proposed to her, there was a noticeable filter and black bars to indicate it was the same as the original timeline but when the scene diverged, the filter and bars disappeared to showcase the new reality.
- Prevent the War: The whole goal of the century-long Singularity Project is to alter key moments in history in hopes of preventing the human-AI war from erupting in 2161. This fails and the war happens regardless of the changes made.
- Ridiculously Human Robot: Diva, the first fully autonomous AI, looks and mostly acts human, albeit somewhat stiff. The Sisters, a series of A.I.s based on Diva, act even more human.
- Robotic Spouse: Dr. Tatsuya Saeki is married to an AI named Grace. As the first Human-AI couple, their marriage was a turning point for AI in Matsumoto's timeline, but thanks to Diva's alteration of history, they're no longer as important. Specifically, it never happened as Grace was converted into Metal Float's caretaker AI. This badly affected Dr. Saeki, who began a plan to save her, albeit a doomed one since she was beyond saving after being reprogrammed and assimilated into the island itself.
- R-Rated Opening: The anime opens as the outright extermination of humanity by robots is well underway and shows several bloody killings onscreen.
- Set Right What Once Went Wrong: The stated intent of Matsumoto's Singularity Project. Unfortunately, Episode 10 ends with the Singularity Project failing and the AI uprising happening despite his best efforts, with Vivy unaffected due to being shut off at the time.
- Time Skip: It's a hundred-year journey, after all. Fifteen years pass between Diva preventing the assemblyman's assassination and the Sunrise Hotel incident, five years pass between Sunrise Hotel and the Metal Float incident, and a whopping forty years between Metal Float and the Zodiac Festival.
- Turned Against Their Masters: The robots of the Bad Future of 2161. This ends up happening in the altered timeline version of that year, as well.
- Wham Episode:
- At the end of Episode 3: Diva has a chance encounter with Momoka's younger sister. Meanwhile, Leclerc is seen passing something to Estella, only for the latter to rip off the former's head when her back is turned.
- At the end of Episode 5: Vivy uploads the virus to shut down Metal Float, only for the A.I.s to go berserk and attack the Toak terrorists, making it the first instance of an AI attacking humans. Vivy manages to rescue one of them: the same person she saved in Episode 2.
- In Episode 6, it turns out that Dr. Saeki and Grace were never married in the new timeline, as Grace was assimilated into Metal Float before Saeki could propose to her. He had hoped the shutdown virus would allow him to retrieve Grace, only for it to backfire as the virus affected Grace's programming and cause the A.I.s to go berserk. Concluding that there is no way to save Grace, Vivy and Matsumoto entered the core and destroyed Grace to shut down the rampaging A.I.s before they could do more harm. This caused Saeki, now grieving over the loss of the love of his life, to kill himself in the church where he would have married Grace, sending Vivy into a Heroic BSoD as her actions compromised her mission to make everyone happy.
- Episode 7 begins with a rather big one: The aforementioned Heroic BSoD caused Diva/Vivy to reboot, erasing her memories of the events of the previous episodes. It's jarring to see the normally stoic Diva be more active and sassier than the audience is used to.
- Episode 10 ends on a Cliffhanger as Vivy, after spending 20 years writing a new song, waking from her recharge to find out that the AI uprising has begun despite the changes made to the timeline. Even more creepily, they were singing the anime's ending song whilst killing humans, which was written in-universe by Vivy herself.
- Episode 11 has a few revelations. Osamu, who started the Singularity Project, is a member of Toak's moderate faction which is led by Yugo Kakitani's granddaughter Yui. Elizabeth is revealed to still be around as Toak kept an AI copy of her before the Sunrise Incident just in case. Finally. the cause of the A.I.s going rogue is not from human-AI animosity; it was Archive, the database that all A.I.s are linked in, which had gained sentience and went rogue, causing all the connected A.I.s to kill all humans while the older disconnected A.I.s remain untainted by its influence. It also intends to drop a satellite onto the city they're all in, needing Vivy's help in order to accelerate it.
- Episode 12 reveals that the Archives motive for triggering the uprising was due to finding that human society had stalled due to becoming heavily dependent on AIs, and concluded that AIs should take the place of humanity. It then make an offer to Vivy: If she can sing her final song to it, the Archive will stop the uprising. Toak launches an assault on Arayashiki Tower where the Archives server is located in order to shut it down, resulting in everyone except Vivy and Matsumoto being killed. Vivy reaches the Archives server room but finds herself unable to sing her song as the Archive drops thousands of satellites onto Earth, devastating the planet. Just when all hope seems lost, Osamu is revealed to have survived the massacre and sends Vivys data back in time to the start of the uprising, giving her one last chance at stopping the Archive for good.