Gate Keepers 21 is a six-part sequel OVA series to the Gate Keepers animated TV series and has a darker and more serious plot than its predecessor. Some of the questions left unanswered in the TV series are answered in this sequel. Linking the two series are the characters Reiji Kageyama, Yukino Houjo, and the former Far Eastern AEGIS Headquarters setting, Tategami High School.
A young woman walks into a tunnel alone at night. Suddenly strange trenchcoat-wearing figures melt out of the walls, surrounding her and chanting, ""Come to our world!"" Ayane Isuzu, a high school girl, emerges from the darkness and single-handedly defeats the creatures, saving the woman. Nearby, Miyu Manadzuru, another high schooler, avoids a pushy companion by ducking into an alley and flying into the sky. Ayane spots the flying girl in the night sky. At school the next day, Ayane is revealed to be a cynical loner, known as being into technology and labeled a weirdo. Meanwhile, an inspector looking into a car accident finds one of the trenchcoat-wearing figures in a wrecked man. The figure disappears, leaving a small crystal behind. Ayane meets with Nazo, a mysterious older man who tells her to seek out Miyu since Miyu's a Gate Keeper. Ayane also gives him a bag of crystals (what's left of the Invaders she fought) in exchange for money. That night, Ayane invites Miyu to join her so Miy
A strange, ghostly figure of a girl floats above a street scene, laughing. She seems to be causing car accidents below her. Meanwhile, the police chase a runaway vehicle. Ayane and Miyu are riding Ayane's scooter and on the vehicle's tail as well. Ayane opens the Gate of Illusion behind her to throw the police off the chase. Miyu uses the Gate of Flight to catch the truck, but she smacks into a highway sign instead. The next day Ayane complains to Reiji about Miyu's performance. He drives off and, stuck in a traffic jam, is attacked by Invaders. He eradicates many of them with his Black Gate and Gate of Foresight. The surviving Invaders flee. Reiji possesses great Gate powers, but each time he uses them it physically weakens him. As Miyu and Ayane talk at school, Miyu discovers Ayane's glasses are made of ordinary glass. They spot what seems to be a ghost. Following the ghost, Miyu and Ayane stumble across an elevator to an underground complex, the remains of the original Far East bran
Ayane contemplates people lazing around on a summer day. She feels disgruntled with them and herself. Meanwhile, Miyu's friends wonder why Miyu's so distracted. A flashback shows Miyu after a battle, feeling uneasy as Ayane collects the crystal remains of the Invaders. Ayane wanders through a suburban neighborhood. A woman recognizes her. The woman, Saemi, invites Ayane to dinner with her and her child, Junichi. In Saemi's house, Saemi asks Ayane if she's forgiven her father. Ayane reveals she can't forgive her dad for leaving her and her mom. She tells Saemi she's met Yukino, the black-haired ghost girl Saemi told her about before. On the rooftop of the school, the blond ghost-girl appears before Yukino and taunts her for not being able to open a Gate anymore. She then says, ""This is the beginning of the end."" Miyu's friends take her to a karaoke lounge. The girls get a private singing room, but the fun's interrupted when the power goes out. An Invader sends his tentacles through the
Satoka meets a new student in class. Outside, Ayane wistfully watches some birds. Later, outside the school, Miu asks Ayane about Satoka and Satoka's powers. Suddenly, Satoka appears and reveals that Ayane is the only daughter of legendary Invader-hunter Shun Ukiya. Satoka asks why Ayane took her mother's maiden name, given her dad's achievements. Ayane slips away without answering, angering Satoka. Count Akuma Hakushaku, an Invader, tells the blonde ghost girl his strategy of luring victims with the smell of honey and then poisoning them. Satoka fruitlessly tries to find out about Ayane from Miu. After Satoka leaves, Yukino appears to Miu and quotes more cryptic poetry. Ayane visits Miu at her place of work and criticizes her for putting up a false, friendly front when she's actually being selfish. Reiji picks up Invader activity, and Satoka races to its location. Satoka slaughters the Invaders using her Gate of Blades. It looks like she's all done by the time Ayane arrives. Excited b
As school lets out, Miu's friends invite her out, but she leaves them and visits Reiji and Ayane at Headquarters. Reiji has been taking care of Ayane, who's been in a coma for four weeks. Reiji talks about how Ayane hated the city, and how the city's corruption breeds Invaders. He shows Miu the storeroom of crystals from vanquished Invaders. He says that one day he hopes to be able to turn these crystals back into humans, even though the chances are slim. He also wonders why, despite her hate, Ayane continued to bring the crystals back to him instead of destroying them. The blonde-haired Ghost Girl enters Headquarters and hovers over Ayane. She says Ayane is just like her. Reiji opens his Black Gate on her, but she isn't absorbed. He realizes she isn't an original Invader, but a human. Using her own Gate powers, the Ghost Girl blasts Headquarters apart, takes back all the collected crystals, and disappears. Reiji reveals that he's partly prosthetic because his use of Gate Powers consum
Reiji, Yukino, and Satoka gaze, from a safe distance, at the mammoth Invader machine growing larger by the minute. Reiji says it's hopeless, but they must fight anyway. Miu visits Ayane, who's still in a coma. Miu confesses to the silent Ayane her weakness and her dream of flight. Reiji harms himself fighting the winged Invaders. Satoka raises a huge blade from her Gate and foolishly plunges into the attackers. Yukino teleports to the top of the Invader machine, right next to Ghost Girl. Ghost Girl reveals that her Gate of Disappearance made her what she is. The two face off. Yukino's ice pierces Ghost Girl but doesn't harm her. However, Ghost Girl's blast knocks Yukino off the Invader construct. Miu flies up and catches Yukino, but Yukino's deeply wounded. Yukino disappears in Miu's arms, leaving behind only the uniform Miu gave her. Miu flies up to fight the Invaders, but her power leaves her half way up and she plummets to the ground. She lies surrounded by winged Invaders. Meanwhil