Masashi Kusakabe moves to a quiet suburban town with his mother, Yasuko, after the sudden loss of his father. He wears a cheerful façade to support his mother, even as sadness lingers in the back of his mind. While carrying boxes into their new apartment, he feels an eerie, unfamiliar presence in the room, foreshadowing an unusual connection to come.
The following day, a strange encounter changes everything. A jellyfish-like creature appears, curious and endearing, and Masashi names it Kurage-bo. The creature loves chee-kama (cheese-and-fish-c cake sticks) and can fly freely, sharing a bond with Masashi that transcends language. Despite the lack of a common tongue, their friendship flourishes, and Kurage-bo becomes a companion that comforts him.
At school, Masashi brings Kurage-bo along in his backpack, anxious about keeping the secret. He soon discovers a startling reality: every classmate has a similar creature, called a F.R.I.E.N.D., and each student uses a small device, the Devices, to summon and control their companion. When the teacher’s attention shifts, the class animates their F.R.I.E.N.D.s, swapping in battles with dazzling speed. A classmate named Tatsuya challenges Masashi, but Kurage-bo intervenes, unleashing a striking display of kung-fu-like skill to defeat Tatsuya’s F.R.I.E.N.D., Yupi, in an impressive showdown.
Back home, Masashi finds his uncle, Naoto, at the door, a researcher who warns that the town may be dangerous. Yasuko pushes back, and Naoto urges Masashi to tell him if anything strange happens. Naoto notices Kurage-bo in Masashi’s backpack but keeps quiet for now, watching the situation unfold.
One day, Masashi wanders past the shrine where his classmates are playing with their F.R.I.E.N.D.s. When the kids push him to join the battle, Kurage-bo is nowhere to be found, and Masashi faces an overwhelming, organized force. Just then, a powerful figure named Luxor appears alongside Kurage-bo, and they join Masashi in repelling the onslaught. Luxor is revealed to be the F.R.I.E.N.D. of a classmate named Saki, who hints at a troubling truth: a top-tier faction from the local research center distributed Devices to all the elementary students, promising “a friend who will never betray.” As the practice of pitting F.R.I.E.N.D.s against F.R.I.E.N.D.s spreads, the town becomes a theater of conflict.
A university festival at the research center becomes a flashpoint. The Black Cloaked Four and a cult tied to Saki’s mother, Shizuko, voice concerns about the center’s experiments, staging protests that blur the line between science and danger. Masashi and Saki slip away together and step into the lab’s orbit, unknowingly drawing the Cloaked Four’s attention. The four mysterious figures decide to trap Masashi, sensing the extraordinary energy he carries.
As Masashi and Saki share their burdens, their friendship deepens. But Tatsuya and Juran, aware of Naoto’s ties to the research center, plot to capture Kurage-bo. When the gym teacher intervenes and punishes Tatsuya and his cohorts for injuring Masashi and Saki in a skirmish, Masashi is left injured and hospitalized. Naoto visits him with a Device offered “as protection,” though something about the gesture feels off.
Masashi’s world tilts when his mother reveals that Naoto has fallen from a building and died. In a forest, Masashi searches for Kurage-bo, only to learn that Kurage-bo has been hidden away in a locker at a junkyard and beaten. Saki finds him and asks where the device is, but Masashi admits the device didn’t work and that Kurage-bo is gone. Together they head to the lab, where a new confrontation awaits.
Inside the lab, Tatsuya and Juran confront Koh, who operates with an unsettling ally named Ko2 and an eerie force that cunningly manipulates others. Yupi and Shimon are killed in the chaos, and Masashi intervenes to save the day. Naoto, who appears as a duplicate, is almost strangling Masashi, until the real Naoto shows up, forcing the clone to retreat. Koh stays behind to locate the Oval’s weak spot as the others rally to call every F.R.I.E.N.D. outside to battle the looming threat.
Naoto explains the deeper motive behind the Cloaked Four: they seek rebirth through destruction, drawing energy from the battles to fuel their own power. He rebukes Tatsuya and Juran for their selfishness and warns them to retreat before the Oval’s power consumes everything. Koh remains vigilant, determined to expose the Oval’s vulnerability, while the others rally their friends to flood the city with F.R.I.E.N.D.s in a final bid for survival.
Saki makes a last-ditch effort to rescue her mother, but she is captured and clings to a metal railing as the Oval opens its ominous mouth. Masashi, ever steadfast, reaches her and carries her to safety. Naoto identifies the Oval’s real weak point—its glowing orb on its head—and Masashi strikes, causing the F.R.I.E.N.D.s to vanish into a vortex, including Kurage-bo.
The loss stings deeply, and Masashi and Saki mourn their friends’ departure. Koh and his allies reconcile with Masashi and apologize for their earlier actions. With a stubborn resolve, Koh uses his device to summon back all the F.R.I.E.N.D.s, restoring them to the world. Reunited at last, Masashi, Saki, Kurage-bo, and the rest find solace in each other and embrace a renewed sense of hope and unity, choosing to foster positivity and friendship in the wake of the trials they endured.
