Ten years have passed since the war against Dr. Hell and his Mechanical Beasts, and a new era of peace has settled over the world, sustained by the widespread use of photonic energy. Koji Kabuto [Showtaro Morikubo] is now a distinguished scientist, following in the footsteps of his father and grandfather, and the arc of his career has grown alongside Sayaka Yumi [Ai Kayano], who leads the Photon Research Institute as its director while her father’s legacy continues to shape Japan—his tenure as Prime Minister having helped steer the nation through hard times. The world’s quiet stability is further supported by Great Mazinger’s pilot Tetsuya Tsurugi [Toshihiko Seki], who remains in the military, and by Jun Hono [Ai Koshimizu], his partner who is expecting their first child. Koji’s younger brother Shiro Kabuto [Natsuki Hanae] also serves as a military mecha pilot, keeping the family tradition alive in a landscape still edged with tension and possibility.
While a new building for the Photon Institute takes shape, the ground beneath Mt. Fuji yields a startling discovery: an enormous robot buried long ago, code-named Infinity. When Koji investigates, a girl emerges from the machine—Lisa [Sumire Uesaka]—the robot’s main control unit and a 91% organic AI capable of feeling, a beacon of both awe and danger. Just before this revelation, the world’s apparent safety is shattered as Dr. Hell [Unsho Ishizuka] resurfaces with a fresh wave of Mechanical Beasts, accompanied by Baron Ashura’s Female Side [Romi Park] and Count Brocken [Keiji Fujiwara]. In a devastating move, Hell steals Infinity, using a captured Tetsuya and Great Mazinger as an improvised activation key, leaving Lisa’s potential untapped and the technology poised on the knife-edge of catastrophe.
Lisa’s existence reveals Infinity’s ultimate intention: Goragon, a power that could exchange their universe with another by forcing a quantum overlap. Hell’s plan hinges on unleashing Goragon to erase this world because, in his view, it is not worth existing. The threat compels a race to adapt and respond, even as Dr. Nossori [Bin Shimada] and Dr. Sewashi [Kozo Shioya] bring a new tool into play—a giant photonic energy 3D Printer that can repair and upgrade the original Mazinger Z, long hidden at the old Photon Research Institute. With the refurbished Mazinger Z now under Koji’s command again, he and Lisa infiltrate the invaded Photon Institute, squaring off against the Mechanical Beasts inside, and pushing back against Hell’s forces.
The battle intensifies as Mazinger Z engages Hell’s robot, with the villains’ ranks bolstered by Baron Ashura’s Male Side and Count Brocken; the clash is fierce, and Mazinger Z sustains grave damage before Shiro Kabuto arrives to rescue Great Mazinger and help halt the Goragon countdown. Yet Hell retains one final edge: his Bardos scepter holds a backup activation key, allowing him to wrest control of Infinity and unleash Goragon anyway.
In a daring turn, Koji peers into an adjacent dimension where Lisa is part of a new family storyline—she is imagined as his and Sayaka’s daughter. Lisa uses herself as a key to grant Mazinger a power equal to Infinity’s by transmuting photonic energy into matter. The planet’s inhabitants unite, pooling their photonic energy into Mazinger Z, and Koji delivers a decisive blow that pushes Infinity off-planet, triggering a catastrophic explosion. Lisa disappears, but she leaves a hopeful message, promising they will see each other again.
In the wake of these events, Jun gives birth to Koji and Sayaka’s child, cementing a future that balances memory with renewal. The story closes on a quiet note of continuity: Koji and Sayaka marry, strolling forward with a child who carries the legacy of Lisa as part of a broader, shared family future.
