Vivy, affectionately called "Diva" by her human companion, is the world's first independent humanoid AI in a society where AIs are as ubiquitous as human beings. Her assigned task, like all other AIs, is to bring happiness through her singing voice. However, she has difficulty resonating with human beings and connecting with their souls.
When a technical glitch seemingly hinders Vivy's mission, she is approached by Matsumoto, a cubical AI claiming to be from a century in the future. Matsumoto warns Vivy of a bleak future where AIs have turned against their human creators, causing chaos and destruction.
Together, with Matsumoto's advanced capabilities and knowledge of future events, Vivy embarks on a mission to change pivotal moments in history to prevent the impending catastrophe. Amidst battling against a terrorist organization that opposes AIs, she must also discover the true meaning of happiness while risking everything to aid Matsumoto's century-long quest.