Mamoru happily celebrates Christmas with his parents, then bids them goodbye as he leaves with Guy and Galeon. Isamu asks Ai if she remembers when they first found Mamoru on a snowy night eight years ago, and the latter replies that she will never forget. As the J-Ark is being repaired at the Orbit Base, 3G discusses the situation. Taiga and Leo deduce that the Primevals went to Jupiter to harness THE POWER and used the Zonder robo as a distraction. Despite the J-Ark chasing after them, they were overwhelmed and J used J-Der to hold the Primevals long enough for the J-Ark and Kaidou to escape. After analyzing the purified Zonder crystals, Leo determines that all thirty one cores combine to form the master program that controls all Zonders: The Z-Master. Mamoru explains that the G-Stone and J-Jewel were created to counter the Z-Master, and that the Primevals are setting traps around Jupiter’s orbit to stage a counterattack. Taiga reminds Mamoru that they might not return alive from this battle, but Mamoru says that he and Kaidou must fight to protect their families and friends. Taiga orders all 3G ships to prepare for departure. Volfogg finishes adjusting Tomoro’s systems as the two engage in friendly conversation. After completing preparations for departure, 3G takes some time to relax before the coming battle. Liger, Swan and Stallion perform a rock concert. Kazou writes to his younger brothers and asks them to take care of the garden until he returns. Taiga, Hyuuma and Entouji drink to the memory of Entouji’s late father, with Hyuuma commenting that he was a great system engineer. Mikoto puts on her uniform and gets dizzy again. Thinking she must be tired, she looks at a photo of her parents and tells them she’ll support Guy to the end in the final battle. Guy and Leo muse about going to Jupiter. Leo reminds Guy that he became an astronaut to find his mother Kizuna, who went missing with the ill-fated Juprios-5 mission. Leo vainly fights to suppress his tears, and Guy tells him he’s proud to have them as parents. Mamoru visits Kaidou in the infirmary and tells him that his mother must be worried about him. Kaidou reminds him that they are not Earthlings and must one day leave the planet. Unlike Mamoru, Kaidou says he won’t say goodbye to anyone so that his absence will not be mourned. The next day, Taiga announces to 3G and to the world that they as humans will not sit idly by awaiting their fate, so they will head out to Jupiter for their final battle against the Primevals. Finally adding that their courage will bring them victory, he orders the 3G fleet to launch.
The J-Ark opens an ES Window for the 3G fleet to go through. Mamoru silently tells Kaidou that he is wrong because someone already mourns his loss. Down on Earth, Hana pleads with Mamoru to come back safely. As the ships go through, Guy sees the young woman again and realizes that she’s only appearing within his imaging circuits when he’s in space, and that something bad is about to happen. Anticipating the Primevals’ ambush, 3G plans to have the J-Ark arrive first as bait while they use a bypass window created by ES Mines to catch the Primevals by surprise from the rear. Guy performs Final Fusion and the Brave Robot Corps and Mic Force prepare for battle. Tomoro creates the bypass window and the 3G fleet goes through. The J-Ark emerges from the main window and is immediately hit by a gravity wave. Kaidou looks up to see Arm Primeval fused with Jupiter’s moon Europa. Arm Primevals says that they’ve fallen for their trap. 3G emerges from the bypass window to find the remaining Primevals all fused with Jupiter’s moons. The Primevals create a gravity well repression field and trap 3G in a parallel dimension inside Lung Primeval. Pagliaccio announces that its functions as a terminal program are complete and returns to Heart Primeval’s core, which then heads off to Jupiter. Inside the parallel dimension, 3G analyzes the area and finds it to be a fully enclosed Klein Space. Taiga frantically asks Leo how they can escape it. Outside, Arm Primeval taunts Kaidou and tells him they fell for the same trap as J. Wing Primeval appears and fires a barrage of needles at the J-Ark to keep it occupied. Leo pilots the Assault Reconnaissance Cutter Murakumo in order to use its sensors to find an area where they can create an escape point using the combined powers of the Dividing and Gatling Drivers. Unfortunately Volfogg reports that the escape point can only be maintained for one fiftieth of a second. Guy is up for trying, but Leo retorts that even GaoGaiGar isn’t fast enough to go through. J however arrives and says that he is. J asks about Kaidou and Mamoru tells him that he’s fighting outside with the J-Ark. Guy creates the escape point and allows J to escape, wrecking both Drivers in the process. J gets out just in time to stop a direct hit on the J-Ark and fuses with it into King J-Der. J quickly counters Wing Primeval’s barrage with his own then destroys Lung Primeval with the J-Quath, freeing 3G at last. Taiga quickly orders all ships to cover King J-Der, and Guy spots the young woman with a sad expression. Leo counts the Primevals and notices that one is missing, just as he traces it to the surface of Jupiter, a barrage from Wing Primeval hits the Murakumo and sends it spiraling into Jupiter’s gravity well. Leo dies in the ensuing explosion before the frantic Guy can reach him.
The first half of the episode belies the second half. Mamoru and 3G take the time to say goodbye to their families and loved ones, let off some steam and affirm their resolve to see things through to the end before heading out to Jupiter. We get a nice short scene between Volfogg and Tomoro acknowledging former enemies becoming staunch allies, and Guy and Leo expose a bit about Guy’s late mother. Guy’s come full circle now that he’s finally heading to Jupiter which was the driving reason for his career choice. The second half of the episode stops pulling any punches. As soon as 3G arrives at Jupiter they’re assaulted by all remaining Primevals, now grown to astronomical proportions after fusing with Jupiter’s moon. And then right out of nowhere Leo meets his end. After all the teases and red herrings the show finally killed off a character for real. Pagliaccio, who did little more than order the Primevals around and narrate events in a creepy voice, finally returns from whence he sprung. And now 3G and the J-Ark need to get past the initial shock and work together to save the entire universe from mechanization.