In Shibuya, five musical groups of teenagers (Leo/need, More More Jump!, Vivid Bad Squad, Wonderlands x Showtime, and Nightcord at 25:00) go about their lives while producing music. They do so with the support of alternate themed versions of Virtual Singers Hatsune Miku, Kagamine Rin & Len, Megurine Luka, Meiko, and Kaito, who reside in Sekai, alternate dimensions made from the group members' emotions, which they travel to using their phones or computers.
Meanwhile, a previously unseen version of Hatsune Miku is traveling between the various screens in Shibuya, looking for help. This Miku's Sekai is a gloomy and unwelcoming void, as the people whose feelings gave rise to it are all experiencing depression and contemplating abandoning their various musical and artistic ambitions, believing they are unable to achieve them. Consequently, this version of Miku is despondent and lonely, and discouraged as she has been trying to connect emotionally through song to the people whose feelings make up her Sekai, to no avail. The lonely Miku seeks the help of the members of all five musical groups, who each help her refine her song and gain confidence in herself. Reinvigorated, Miku once again attempts to reach out in song to the people whose feelings formed her Sekai, but is again met with failure.
As the individuals whose feelings formed her Sekai fall further into their depression, Miku grows more desperate and begins to lose hope. At the peak of her despair, Miku transports all five of the groups into her Sekai. As they travel to Miku's lonely Sekai, the groups witness scenes of each of the people whose feelings created it struggling in their daily life. They attempt to persuade Miku to not give up, but are unsuccessful. Miku tearfully thanks them for their efforts and sends them away, and her lonely Sekai is swallowed in an ocean of darkness, which also permeates the other five Sekais and engulfs each of the groups' versions of Hatsune Miku, making them all disappear. The Sekai's collapse causes an unusual blackout throughout Japan, and the groups subsequently discover that all traces of Miku's voice in songs and elsewhere have disappeared from the real world.
The five groups each realize the connection between the depressed people in the real world and the Sekai, and come to the conclusion that the only way to save the lonely Miku and restore their own Mikus to existence is to cheer up the people whose feelings formed the lonely Sekai. In order to do this, they resolve to publicly perform new songs which they hope will reach the people and ameliorate their depression. They do so, and are heard by each of them, resulting in the ocean of darkness subsiding from the lonely Miku's Sekai and the restoration of the other Sekais' Mikus. Now empowered with renewed hope, Miku reappears and performs her song for all of Shibuya, and this time successfully connects emotionally with the populace.
After the performance, the now optimistic Miku teleports the groups to her Sekai, which is now bright and filled with hope, and thanks them for helping her complete her song. The groups bid Miku goodbye and all return to their normal lives. Later, one of the people whose feelings created the new Miku's Sekai visits her, and she greets them, saying happily that she has been awaiting their arrival.
