Kagami Arata, member of ZECT, meets Tendou Souji, who has been training his entire life waiting for the Kabuto Zecter. As a Worm attacks a young girl, Kagami attempts to call the Kabuto Zecter but it flies to the hands of the strange man, Tendou Souji.

Tendou uses the second form of Kabuto, known as "Rider Form" by using a process called "Cast Off". Kagami tries to understand Tendou and why he believes he is destined to be great.

A woman named Yuki is attacked by the Lanpyris Worm and impersonated, but she survives so now there are two Yukis running around. More intrigue between Tendo & Kagami, who is quickly falling out of favor with ZECT, plus a fight between Kabuto and a new kind of Worm at an amusement park.

Sou Yaguruma, also known as Kamen Rider TheBee, arrives from ZECT HQ with his own ZECT Tropper team known as Shadow. Kagami warns Tendou to stay out of ZECT affairs now that a new Kamen Rider is here. After saving a wedding and fighting a pair of Worm, TheBee then asks Kabuto about joining them and ZECT, but Kabuto refuses, resulting in a showdown between the Riders.

Kagami must face the tough truth about the person his younger brother really is. Tendou confronts Kagami and tells him that he will defeat all Worms, including Kagami's brother, Bellcricetus Worm. In the end, Kagami is left with the toughest choice of his life.

The connection between Hiyori and Tendou is seemingly discovered as Tendou makes a promise to Hiyori that he might have to break after ZECT discovers the identity of Kabuto.

Tendou plans his escape from ZECT with the help of Kagami. After escaping, Kagami is sent to meet Hiyori and Tendou must defeat two Worm that are impersonating ZECT members.

Due to being upstaged by Tendou, Yaguruma loses his cool and begins trying to defeat Kabuto once and for all. After seemingly destroying the Zect Belt, Hiyori remembers more about her past and the boy that had a rider belt.

Yaguruma discovers that Tendou is alive and well, and so is the Zect Belt. Furious, he and Tendou fight once again, but this time, Yaguruma goes insane and injures his fellow comrades in the process. Ideals lost, the TheBee Zecter leaves him for Kagami Arata.

Kagami basks in the power of the TheBee Zecter and the new position of Shadow's captain. However, his mission is to defeat Kabuto and after fighting him, Kagami realizes that there is something far more important to him than being a Rider. After this, he gives up the TheBee Zecter along with the title of Kamen Rider TheBee.

Tendou constantly tells Kagami that he has forgotten something important. Kagami does not understand this, but after being saved from a Worm, Tendou asks him why he joined ZECT. Kagami, still puzzled, watches in shock as Kazama Daisuke, a makeup artist, transforms into Kamen Rider Drake.

Tendou and Daisuke have a contest to see who can get the most girls to follow them in one day. Despite that Tendou did nothing but scratch cards all day, he wins the contest as all the girls collected by Daisuke run to Tendou because they all know who he is. Kagami finally realizes that Tendou was trying to tell him to remember his promise to fight Worms.

Yaguruma returns with a new vigor and is determined to protect Shadow because someone has been killing off Shadow members one by one. Kageyama believed it to be Yaguruma who was doing the betrayal, but in the end this was proven false. However, Kageyama is now the user chosen to be Kamen Rider TheBee.

Kagami is marked as the traitor by Kageyama, and is chased across town by the entire team of Shadow. This seemingly perfect case is broken when Kageyama reveals that he was just using Kagami as bait to lure out the real traitor. A Zect operative shoots Kagami who is saved by Tendou at the last second, who reveals that one of Kageyama's troops is actually the traitor, the only one who could see him when he Clocked Up to save Kagami. In the end Drake, TheBee, and Kabuto have a three-way battle.

Kagami feels betrayed by ZECT and takes a leave to try and solve his own mission. Drake and Kabuto secretly back him up and they discover that there are multiple Worms impersonating the same person, and they do not try to kill each other. Tendou joins ZECT in order to find out more about this, and automatically becomes Shadow's leader.

Realizing that there were three Worms mimicking the same man all along, Drake and Kabuto work together to defeat them. Kagami thinks that he destroyed a Worm by himself, but in truth Tendou has helped him through the use of Clock Up. Mishima temporarily takes over as TheBee because Kageyama failed to do his job.

Gon is hurt as Daisuke constantly ignores her and mistreats her, and so she runs off to Hiyori. However, after being attacked by a Worm, she hits her head and recalls some of her memories. In the end, Gon gets captured by ZECT.

Due to an attack by a Worm from Gon's past, Gon's memories are restored, at the cost of losing her memories of being Gon; and with Daisuke. She returns to her mother and Daisuke leaves for an unknown place, realizing that it was for the best.

A new man by the name of Tsurugi Kamishiro appears, and he is seemingly as arrogant as Tendou. After competing with Tendou in all manners of sports, he meets Tendou at the top of the roof, ready to fight a Worm. It is then shown that he is Kamen Rider Sasword.

Tsurugi becomes the next target of the Phantom Thief Shadow, whose actual goal is to lure the Worm that only targets criminals out. Tsurugi causes a traffic accident which injures Juka, and so Tendou punches him. After realizing Tendou also has a sister, he apologizes. After destroying Sepultura Worm with Rider Slash, Sasword transforms into Scorpio Worm, the very Worm that killed his sister.

ZECT has made a new Zecter known as the Gatack Zecter. Due to its immense power, no one is able to use it and Tadokoro is badly hurt trying to tame the Zecter. Elsewhere, Kagami has made friends with a young boy who seems to be hiding something.

Kagami tries his hand at taming the Gatack Zecter but is badly hurt in the process. After discovering the secret of the young boy Kagami met, he is seemingly killed, until the Gatack Zecter is placed in his hands. Using its power, Kagami is able to become Kamen Rider Gatack. Kagami wins his first battle and also discovers that all Worms are not necessarily evil.

Worms begin attacking anyone and everyone that possesses pieces of the meteorite. Kagami questions Tendou as to how he originally came into ownership of his belt and the truth about the financial state of the Discabil family is exposed.

Tendou and Tsurugi finish their battle from the previous episode to end with Tendou as the victor. Hiyori, along with Kagami and Tendou, enter Area X to discover what ZECT is trying to keep hidden from the world. Once inside, the trio meets resistance from Kageyama and Shadow and Hiyori discovers that Tendou and Kagami are Kamen Riders Kabuto and Gatack. After receiving some help from an unlikely ally, the trio opens the door to the center of Area X.

The stay inside the core of Area X is cut short as TheBee and Shadow force the trio to make an early exit. Tendou joins the police force in an attempt to get closer to ZECT and Kagami impersonates Tadoroko to get closer to ZECT HQ. Meanwhile, as Kageyama pursued a new and mysterious Worm, Rena Mamiya/Uca Worm, one of her subordinates assumed Misaki's form to kidnap Tendou's younger sister, Juka.

Tendou and Kagami try to find out why Kagami's name was written in the file from 35 years ago. Tendou is questioned about the identity of his parents and Hiyori begins to suspect Tendou of being more than he claims to be.

After holding off a very powerful Worm that Tendou is unable to beat, he makes a promise to Hiyori that he will always protect her. Elsewhere, Gon regains her memory after reading an article about Daisuke, who has been accused of a murder. Jiya then falls ill and a grieving Tsurugi goes to Tendou for help.

Everyone thinks Daisuke has died and that a Worm is impersonating him, but in reality it was a deception to force the Riders on one another. The real Daisuke was soon attacked by the other four riders as he tries to prove that he is human. Eventually the Worm's identity is discovered, and Daisuke retrieves his Drake Grip. Hyper Kabuto makes its first appearance after defeating several Pupa Worms.

A new Worm under the guise of master chef Ichiro Ikesu is using the dark cookings arts to have people submit to his "superior" skill as part of his plan to rule the world with his cooking added with the power of the Black Knife. Jiya then tries compete against Ichiro Ikesu without knowing that he is a Worm, Jiiya falls ill after losing to him in an iron chef match. Tendou vowed to avenge Jiya.

Tendou pays a visit to Jiya's brother and receives the ancient White Knife blade that will allow him to win in the upcoming match with Ichiro. Kagami then discovers the shocking truth behind Tsurugi's past and must come to his defense against a Tendou who says that he will defeat all Worms.

Kagami tries to learn more about how Tsurugi became a Worm, eventually he ends up at Jiya who has a secret that he has been keeping from Tsurugi. For helping him in a battle, Tsurugi proclaims that he and Kagami shall now be best friends. Hiyori, after being attacked by a group of Worms, evolves into Sisyra Worm, her true form.

Hiyori finally discovers that she and Tendou and are brother and sister. Hiyori has become the target of ZECT with Mishima commanding Kageyama to eliminate her. Mishima is also seen with the mysterious Hyper Zecter. Tendou, Kagami and Hiyori finally enter the center of Area X, but Kagami and Tendou are thrown out onto a beach while Hiyori discovers the identity of the man in the iron mask.

Hiyori disappears and Tendou lends his strength to ZECT to find out where she has gone. A training session is held for the new ZECT Troopers and a girl named Renge Takatori is sent by Mishima to get closer to Tendou. Tendou also starts collecting the Zecters to ensure that he will be the only rider left, but after attempting to obtain the TheBee Zecter, he meets an old Rider, with a new look, who has become Kamen Rider KickHopper.

Kageyama begs Tendou to return him his Zecter but Tendou says he will be the only rider in the end. Afterwards, Mishima orders Renge Takatori to kill Tendou; but when Tendou convinces her to eat his cooking, she steals the Hyper Zecter from Mishima only to be pursued by both enemy factions. The Hyper Zecter is then seemingly destroyed, and Kagami was destroyed by the worm. It turns out, the Hyper Zecter merely warped itself through time to come to Tendou allowing him to transform into Kamen Rider Kabuto Hyper Form. He uses it to return to save him just before Kagami was destroyed.

A mysterious man called Daigo Tachikawa tells Tendou to stop collecting the Zecters. He says the riders are there to combat Worms that aren't native to earth. Daigo becomes Kamen Rider Drake later on to save a mother and her child in front of Kagami. After being told to chase Daigo, Kageyama is nearly killed when Yaguruma saves him and "sends him to hell" allowing him to become Kamen Rider PunchHopper.

Riku Kagami tells Tendou of the story of The Red Shoes and explains that both Kabuto and Gattack has a system that forces the wearer to destroy all Worms, regardless of the wearers' will. After Kabuto goes insane and almost kills Tachigawa, Gatack stops him but is unable to prevent Daigo's death by Cochlea Worm. In the end, Tendou and Kagami make a pact to stop each other if they ever try to destroy Hiyori.

Tendou learns of strange occurrences happening at Juka's school and sends Kagami and Misaki to investigate the problem. Kageyama encounters a young girl who he protects and is reminded by Yaguruma that he can no longer interact with other humans.

The truth behind the school's ghost story is discovered, for the principal has been making secret deals with the Worms, who in turn replace students, one by one. Kagami seeks out this Worm after going on Juka's trip, and Tsurugi returns, once again as Sasword.

Uca Worm seeks out Tendou once more, in an attempt to retrieve the Hyper Zecter, but her plan is foiled when she loses her memory due to Tendou's Hyper Sting attack. Befriended by Kazama Daisuke, she seemingly returns to her normal life of singing and happiness. Kabuto is taken to an alternate dimension and meets Dark Kabuto.

Rena recovers her memories after encountering Punch and KickHopper, but was saved by Kamen Rider Drake. After becoming Uca Worm again, she proceeds to fight Drake, but is forced into a weak position. After sacrificing his love for her to come to the realization that she was evil, Drake makes a heart-paining choice and destroys Uca Worm.

A new weapon is created by ZECT called the AM bomb. Short for anti-mimicry, this device is used on the general population, revealing all the Native's and other Worms disguised as humans. Kagami also goes to his father and learns the origins of ZECT and the Masked Rider system, wondering if his sole purpose is to fight Worms.

Reiji Nogi has captured mass amounts of Native Worms along with Tadakoro. He demands that one more AM bomb be given to him. If so, he will release the Natives, however, they will no longer have their mimic abilities. Kagami is sent into negotiations, but things happen that are even out of his control. Meanwhile, an old dark enemy returns again to take on Kabuto.

The Worm Souji has appeared in the city and after visiting the Bistro and trying Renge's food, Kagami notices something odd about him. They realize he is a Worm, but Hyper Kabuto is able to subdue Dark Kabuto. However, Hiyori appears and sides with Dark Kabuto. Nogi and his Worm forces also prepare to enter Area Z, the location of the Masked Rider System's creation.

fter hearing that Hiyori does not want to return to the real world anymore, Tendou is left in shock. Kageyama begins to stray from the path of darkness as he is enticed by the sight of TheBee. Elsewhere, Nogi and his army advance towards Area Z. Kagami holds off Nogi's forces while Tendou tries to convince Hiyori to return to the real world.

The Worm Souji returns to the real world to destroy everyone and everything, including Hiyori. Tsurugi and Misaki prepare for their first date, but while on their date, Tsurugi becomes Scorpio Worm. Tendou and Kagami prepare themselves for the approaching battle with Dark Kabuto.

Kamishiro Tsurugi finally becomes aware that he is Scorpio Worm. Driven to a point of insanity, he takes Kagami captive and demands that all the Zecters be given to him. Tendou then goes to make the trade, but ultimately defeats Scorpio Worm.

Riku Kagami has finally announced to the world the threat of the Worms, and in turn ZECT has created necklaces that react when a Worm is nearby. However, Tendou seems to be destroying these necklaces, but will not tell anyone the reason. In an attempt to block Tadokoro's bullets, Tendou accidentally injures Renge.

After confronting Tendou about the truth of the Worm necklaces, Kagami doesn't believe that they actually turn humans into Natives. Tendou and Kagami once again fight, with Kagami being the victor. Meanwhile, Mishima is plotting with Negishi to overthrow Riku as the leader of ZECT. Yaguruma is forced to kill Kageyama after he turns into a Native, due to the necklaces.

Kagami rushes to stop Mishima's plans of using a meteorite to drain Dark Kabuto of his powers. As he reaches the area of the final battle, he finds Mishima and Negishi conducting a broadcast all around the planet. Unbeknown to the humans, the signals sent out by the broadcast are composed of Dark Kabuto's drained power and causing the humans to become Natives. As Kagami lays defeated, Tendou appears, after going one-on-one with Mishima, Kagami regains his strength and joins Tendou in a double team on Mishima for the final battle.