Long ago, the Gurongi Tribe terrorized the Linto (リント Rinto) until a warrior named Kuuga appeared and defeated the Gurongi, sealing their leader within a cave. In present day, a multi-talented man named Yuusuke Godai finds himself linked to the mysterious stoned belt that was found within the excavated cave as the Gurongi are resurrected and resume their murderous game on the descendants of the Linto, humanity itself. It is up to Yuusuke, along with the assembled Science Police, to use the various powers of Kuuga in order to stop and defeat the Gurongi Tribesmen from their continuous killing and ensure the happiness of others. However, as endgame draws near, Yuusuke learns that there is a horrible revelation behind Kuuga and the Gurongis' leader.
A man named Shouichi Tsugami has lost his memories. He doesn't know who he is, where he came from, or how he came upon his peculiar circumstances. Tsugami, seemingly for no reason, transforms into a powerful superhuman, Agito, whenever in the presence of the beings referred by the police as the "Unknown", a race of powerful monsters that have been causing murders around Tokyo, targeting certain people as their prey. In response, the police department unleash their newest weapon: the G3 powersuit, originally developed to fight against the "Unidentified Lifeforms", the enemies of No.4 (Kamen Rider Kuuga). G3 and Agito don't know whether they should join up and defeat the Unknowns, their common enemy, or to combat each other, keeping the mysteries that entwine them separate. Ultimately, even more mysteries unfold, with the appearance of Kamen Rider Gills, who is on a search to uncover why his father committed suicide. These mysteries and others collide, as the true nature of Agito would ultimately determine the fate of humanity.
Thirteen Advent Card decks were created for thirteen Kamen Riders. They make Contracts with monsters from the mysterious Mirror World (ミラーワールド Mirā Wārudo), a parallel dimension opposite to our own in which only the Kamen Riders can exist. The Riders draw on their monsters' strength in exchange for feeding them the life force of the creatures they destroy. The creator of the Advent Cards has only one rule: that there can be only one Kamen Rider. The others must be killed, and the sole victor will be granted a single wish, which leads to a conflict known as the Rider Battle.
All over the city, innocent people are being mysteriously abducted, never to be seen again. During his investigations of these incidents, Shinji Kido – an intern at the online news service ORE Journal – discovers one of the Advent Card decks at an apartment where every reflective surface has been covered by newspaper. He is soon sucked into the Mirror World, discovering the terrifying truth behind the disappearances: people are literally being pulled through mirrors by the monsters of the Mirror World so that they may feed. He is about to be killed by a powerful dragon named Dragredder when he is saved by Kamen Rider Knight: Ren Akiyama. Ren seeks to win the Rider War at all costs. He works with a young woman named Yui Kanzaki, who seeks her missing brother: the master of the Rider War, Shirō Kanzaki. Seeing Ren's strength, Shinji enters the Rider War not for the prize, but so that he may protect innocent people from the threat of the Mirror World, and stop the senseless fighting between the Kamen Riders. With Dragredder as his Contract Monster, he becomesKamen Rider Ryuki.
The Smart Brain Corporation, the world's most powerful corporation, is trying to take over the world using Orphnoch, the next stage in humanity's evolution, to covertly kill off the human population. In pursuit of this, they develop three suits of power armor, called Rider Gear (Delta, Faiz, and Kaixa), to find and protect the Orphnoch King, who can fix a defect within Orphnoch DNA which causes their genetic structure to break down, leading to death.
The Rider Gears are stolen by Hanagata, the Goat Orphnoch and former President of Smart Brain Corporation. He sends them to his foster children (dubbed the Ryuseiji, after the school they attended) so they can stop the Orphnoch from achieving their goal. However, Rider Gears were designed to be worn by Orphnoch, and humans are unable to activate the systems without undergoing genetic modification.A young loner, Takumi Inui, is unwillingly drawn into the conflict between the Orphnoch and humans and becomes Kamen Rider Faiz to save the life of Mari Sonoda, one of the Ryuseiji. The Smart Brain Corporation begins targeting him in an attempt to retrieve the Faiz Gear.However, there is division amongst the Orphnoch, as those who wish to co-exist with humans rather than kill them, begin resisting Smart Brain, who in turn targets them as well. Most of these "renegade" Orphnochs are either killed, remain neutral or begin siding with the Ryuseiji against the Smart Brain Corporation.When the Tokyo police discover the Orphnoch are behind a series of bizarre murders, they begin operations to defeat the creatures, largely unaware of the various factions involved. They even begin performing experiments on captured Orphnoch in an attempt to find ways of destroying them, though this does not go well.The Orphnoch King eventually awakens within a young boy named Teruo, whom Naoya Kaido and Keitaro Kikuchi saved and befriended. Now, it is up to the holders of the Rider Gears to band together and fight for humanity's survival.
Ten thousand years ago, a massive battle known as the Battle Royal was fought by fifty-two Undead, each representing a species fighting for dominance over all others. The winner was the Human Undead, known as Category Two of Hearts, giving dominion of the Earth to humanity. In the present day, archaeologists discover the sealed Undead, and accidentally set them free. Thus, a new Battle Royal begins.Having developed the Rider System, based on the Joker's ability to copy sealed Undead, the organization BOARD (Board Of ArchaeologicalResearch Department) equips two young men, who become Kamen Riders: Kazuma Kenzaki and Sakuya Tachibana fight together asKamen Rider Blade and Kamen Rider Garren to protect humans from Undead and seal them. Also fighting Undead is the mysteriousChalice, a Kamen Rider whose purpose is unknown. In addition, a young man struggles to free himself from the control of the sealed Undead powering his own Undead-made Rider System, fighting as Kamen Rider Leangle.
The Kamen Riders, known as Oni, battle man eating beasts called Makamou with "pure sound". One of the Oni, a man named Hibiki ends up having a teacher and apprentice-like relationship with Asumu Adachi. A young boy unsure of himself and is at a crossroads in his life as he transitions to high school, Asumu learns to be an adult through watching Hibiki and the other Oni as they all train together to hone their skills in fighting the Makamou and the homunculi aiding them. However, the sudden raise of Makamou numbers proves to be a prelude to an upcoming calamity.
The story revolves around a man named Souji Tendou. He has trained seven years while waiting for the Kabuto Zecter so that he may properly take up the name of Kamen Rider Kabuto. Making many enemies while at the same time meeting other Riders with mysterious origins of how they got there, Tendou attempts to accomplish his goal at all costs: destroying all Worms that otherwise threaten humanity. He meets Arata Kagami, who later becomes Kamen Rider Gatack, the two work together to save humanity from the alien Worms that arrived from a meteorite seven years ago.
Ryotaro Nogami is a young man with a lot of bad luck. One day, he finds a strange pass and things got stranger from a mysterious girl and a large time-traveling train to being possessed by an entity called an Imagin, beings from an alternate future whose kind are attempting to change the past. Though slightly confused about the nature of the crisis, Ryotaro, along with the aid of the hot-headed, violent Imagin, dubbed Momotaros, becomes Kamen Rider Den-O, traveling to different times on the DenLiner to battle the evil Imagin to prevent them from altering the past to affect the present and future. During his adventure, Ryotaro is joined by other Imagin who aid him as well; the lying, manipulating and womanizing Urataros, the herculean (and narcoleptic) Kintaros, and the childish yet powerful Ryutaros. He later meets the mysterious Yuto Sakurai and his bumbling Imagin partner Deneb. Yuto is not only Kamen Rider Zeronos but is the younger incarnation of Ryotaro's older sister Airi's fiance, Sakurai, who mysteriously disappeared and is tied to the mysteries involving the Imagin and a person known as the Junction Point.
Twenty-one years after the disappearance of his father, Wataru Kurenai lives in an infamous "haunted house" where he is destined asKamen Rider Kiva to fight life-draining monsters called Fangires, the very race his father fought years ago before his disappearance. Wataru must also deal with Kamen Rider Ixa who is part of an organization seeking to destroy the Fangire menace, as well as the Fangires' own Rider, Kamen Rider Saga. The story is split between the actions of Wataru in the present (2008-09) and his father Otoya in the past (1986-87), slowly revealing the link between the Fangire Race and Kiva.
The story revolves around the nine previous universes of the Heisei Kamen Riders merging into one, something that would destroy all the worlds. To prevent this, Tsukasa Kadoya transforms into Kamen Rider Decade and is told that to protect his own world he must travel with Natsumi and her grandfather to the other Kamen Riders' Worlds called A.R. Worlds (Another Rider's World or Alternate Reality World) and eliminate the anomaly in that world. Along the way, confronting the mysterious Narutaki and the thief Daiki Kaito, they are joined by Yusuke Onodera of the World of Kuuga and Kivala of the World of Kiva.
In the ecologically-minded city of Futo (風都 Fūto, the "Windy City"), there are many windmills and the people live in harmony. However, the Sonozaki Family sell mysterious devices resembling USB flash drives called Gaia Memories to criminals and other interested parties who use them to become monsters called Dopants, committing crimes with the police force powerless to stop them. To make matters worse, the Gaia Memories carry a dangerous toxin that cause their users to go insane to the point where they could die from the life-threatening devices. After the death of his boss, the self-proclaimed hardboiled (actually half-boiled) detective Shotaro Hidari works with the mysterious Philip, who possesses the true Gaia Memory, to investigate crimes which involve Dopants. Using their own Gaia Memories, Shotaro and Philip use the Double Driver belts to transform and combine into Kamen Rider Double to fight the Dopant menace and keep Futo safe. While joined in their fight by investigator Ryu Terui, who transforms into Kamen Rider Accel, the mystery of Philip's past and his relation to the Sonozaki Family and their Museum organization are revealed.
Eiji Hino is a man who has no dreams, no job, and no family. When animal-like monsters called Greeed awaken after their 800 year slumber to attack humans and feed off of their desire, a bird-type Greeed called Ankh gives Eiji a belt and three Medals to fight the Greeed. This allows Eiji to become Kamen Rider OOO. The mysterious Kougami Foundation approaches him and begins assisting him in his fight against the Greeed, but their true motives are not clear. When Eiji fights for the first time, he starts to realize what it means "to be alive".
