Daiki Kaito (海東 大樹, Kaitō Daiki?, portrayed by Kimito Totani) is a mysterious young man who is portrayed as being cheerful to the extent of being annoying to those around him, but becomes serious in battle and sees material objects as more important than anything else. Narutaki, aware that Daiki is Diend, avoids getting in his way. He also appears to know about Tsukasa's past, referring to sea cucumbers as being something Tsukasa had always wanted to taste. He travels from A.R. World to A.R. World, stealing what he refers to as "treasures". Daiki's surname is ahomophone of the Japanese word kaitō (怪盗?, phantom thief), a role he fulfills in Decade.
It is revealed that he comes from an A.R. World (referred to as the "World of Diend") where he was an officer who served the evil Fourteen who has deemed Kamen Riders as threats to the public peace. Daiki hunted them down and turned them in for education until he captured the leader of the Kamen Riders: Kamen Rider Glaive. When Glaive is unmasked, he is revealed to be Daiki's older brother Junichi.
By then, Daiki learns the truth that Fourteen brainwashes people, powerless to stop him. Losing his self-confidence and seeking to undo all of the mistakes he had caused, Daiki had stolen the Diendriver from Dai-Shocker, becoming Kamen Rider Diend and becomes Fourteen's new most wanted Kamen Rider.
He leaves his world, traveling to other worlds and taking their treasures as a means of self-delusion until he crosses paths with Kamen Rider Decade. Eventually, he does lackadaisically accept the Hikari Studio residents as "friends", even calling Decade a "comrade", though he is not beyond abandoning them without explanation, usually for his own self-interest.
Though he briefly appeared in Blade's World, revealing he knows Tsukasa, Daiki found nothing worth taking. Arriving in Faiz's Worldahead of Tsukasa, Daiki witnesses Faiz's battle with the Butterfly Orphnoch and was unable to catch him to acquire his Faiz Gear. When Tsukasa arrives in Faiz's World, Daiki reveals that Faiz is among the student body and warns him not to meddle in his affairs. However, as Tsukasa decides to find Faiz, Daiki gets Lucky Clover's aid by showing them the photograph that Faiz dropped during the fight under the assumption he wanted to join their group, leaving them to attack Yuri before Takumi becomes Faiz to protect her. Daiki then attempts to run away from school, but realizes that he needs to stay and make sure the belt is in proper hands.
When the Orphnochs acquire the belt, Daiki reveals his true intentions as he becomes Diend. He kills the Centipede Orphnoch before he and Decade fight over the Faiz Gear until Takumi regains it, later disposing of it. But in spite of being told Takumi had something more precious than the Faiz Gear, Daiki takes the Ride Booker from Tsukasa in an attempt to take the Faiz Gear from him. Narutaki whisks Tsukasa away to fight Kamen Rider Ryuga, but Daiki interrogates Kivala on the location to save Tsukasa, claiming that the Faiz Gear is what he came from as he gives Tsukasa back his Ride Booker.
However, during the Lucky Clover invasion of the Smart Brain School, Daiki returns once again to Tsukasa and Takumi's aid, returning the Faiz Belt to Takumi. After the fight, Daiki claims the Orga Gear for himself out of rubble while seeing it as the "more precious treasure" Tsukasa spoke of, leaving a little note on the painting ofAgito's World as a warning not to meddle in his affairs again, which further irritates Tsukasa.
In Agito's World, Daiki is training along with Yuusuke and others to become the next G3-X user. Acquiring the position, it is only revealed later that Daiki's real goal in Agito's World is to steal the newly-created G4 chip that was stored in Ashikawa's locker, Yuusuke confronts him until Toko arrives and blasts the chip to bits. Daiki later aided Yuusuke in protecting Ashikawa, only to find out what he possessed to be more precious than the G4 Chip. However, seeing that to be his Agito powers, Diend leaves the fight scene to the next world as he could not take it with him.
In Den-O's World, Kaito attempts to coax the Imagin Momotaros, who took Yuusuke's body, into allowing him to use a Final FormRide card on him to become a DenLiner. When M-Yuusuke refuses, he is ran ragged by Diend to leaves him to reconsider his offer.
However, when he offered again, Decade takes the card from Diend while defending Momotaros before helping him regain his and self and form. Sticking around Den-O's World, Diend sneaks aboard the DenLiner to the past where his summoned Riders were used by Urataros, Kintaros, and Ryutaros.
In Kabuto's World, interested in the Clock Up ability of the Kamen Riders, Diend saves Decade from TheBeeand Gatack, fighting the latter by himself as he is further impressed by the Clock Up System and proceeds to get it from Kabuto. But after the attempt blew up in his face, Daiki receives a "treasure" from Tsukasa which was actually a vial of pepper. In Hibiki's World, after an attempt to rob Hibiki, Daiki learns from Asumu of the three scrolls owned by the three Oni schools. Working his way in Zanki's school, he makes a preposition to aid him in settling things with Ibuki and his school.
However, during the fight with Decade, Diend reveals his true colors after stealing the Zanki and Ibuki school scrolls and having Momotaros cover his escape. He then admits to get the last scroll from Hibiki who blocks his path and gives him his Onkaku to give to Asumu along with his final request. The next day, Daiki uses Asumu to distract Hibiki lost enough to steal the scroll, invoking the man's change into Gyuki to cover his escape.
However, after reading the scrolls, Daiki returns to give Asumu the Onkaku in order to see the harmony of the three Ongekidō styles. He takes his leave soon after, though thanked by Asumu and the others in spite of his protest that his motives were selfish. He is seen again in the Negative World, following Tsukasa before he overheard Otoya speaking of treasure that attracts the thief into fighting alongside Decade against the Dark Riders. Though he gained the treasure (through the use of paper airplanes), the K-Touch, Diend loses it during the fight.
Returning to the his home world Daiki meets up with his old friends Haruka and Shin as they fight Darkroachesas Larc and Lance, the latter blaming him for Junichi's brainwashing. Tsukasa approaches Daiki after Natsumi and Yuusuke have also been brainwashed by the evil Fourteen, and Daiki agrees to help Tsukasa, Haruka, and Shin defeat Fourteen and his brother who can transform into Glaive.
Together, they reveal Fourteen's true form as Jashin 14 and destroy him, freeing everyone from brainwashing. However, Junichi revealed he was never under Fourteen's control and was working for him on his own free will. Diend and Glaive fight, though neither has the will to kill the other, especially after Tsukasa tells them that brothers must look after each other, no matter what.
Junichi and Daiki go their separate ways as Daiki travels to the next world, with the intent to obtain theShinkengers' Origami. Starting with Genta Umemori'sIka OriGami, Daiki runs off with Genta in pursuit. Deciding to fight him as he cannot lose him, Daiki gets an unexpected visit from Chinomanako who steals his Diendriver and hounds him until he makes his way to Tsukasa who has Yuusuke take him back to the Hikari Studio. He evantually gets it back from ShinkenGold when Chinomanako is destroyed by the combination of Decade, Kuuga, and the Shinkengers in exchange for the origami he stole.
Diend is next seen in RX's world looking for something to steal. When Decade is knocked into Black's worldKaito fends Black off with the power of Kamen Rider Femme. Diend manages to steal the Perfector from Decade and re-enter RX's world. Decade follows and Diend hands over the Perfector after a huge battle between themselves, RX, Black, and Dai-Shocker's Apollo Geist telling Tsukasa to save Natsumi and that there are other treasures to steal.
In Amazon's world Diend appears again looking for the GaGa Armlet. Diend manages to infiltrate the Dai-Shocker base and learns the armlet is in possession of Llumu Qhimil. He joins Decade and Amazon in a fight against the ten faced demon and after GiGi Armlet is stolen from Amazon, Narutaki presents Kaito with a card that will make Diend stronger on the condition that he defeats Decade. Kaito takes the card but says that there are other options as well.
Kaito then appears to tell the Hikari Gang that the boy who stole the GiGi Armlet, Masahiko is being subjected toDai-Shocker's Human to Monster project. Diend then battles with Decade and Amazon having recovered the GiGi Armlet and manages to steal the GaGa Armlet from Llumu Qhimil until Decade uses an Attack Ride Card to take it from him. The riders then destroy Llumu Qhimil and Diend joins the Hikairi Photo Studio as a traveling partner into another world. They end up in the worst possible world as they enter the World of the Rider Warfrom Natsumi's nightmare.
In the World of the Rider War Diend helps Asumu kill off Saga and his Fangire Minions. Asumu explains to Daiki that there are some treasures that should never be taken. When Tsukasa goes to save Natsumi, Kaito appears to tell him about the trap Super Apollo Geist has planned but Tsukasa goes anyway, promising Kaito that if he dies Kaito can have the world. Diend helps Tsukasa fight Super Apollo Geist and the revived Kaijin even giving him a Diend Final Attack Ride to destroy Geist. But when the Rider War commences he shoots Decade at point blank range marking future battles.
After Decade is destroyed he and Natsumi meet Wataru Kurenai who explains Decade's role as a substitute for the riders of the A.R. Worlds. When Tsukasa is revived Diend joins the fight against Super Shocker. After the struggle he is seen with the Hikari Studio gang posing for a picture.
He allows the Spider Imagin to be destroyed and hitches a ride back in time on the DenLiner to attempt to cause a time paradox so he can be arrested byKamen Rider G Den-O. This sets in motion events that would allow him to complete his plan, by getting his future self killed, but being able to steal the past iteration of that same gun, putting it into his possession the entire time and preventing his own death. It is also during this trip to the past that his past self saves Reiji Kurosaki, who entrusts the past Daiki with the K-Touch and allowing him to become Complete Form.
In some materials in Decade, Daiki's surname is spelled in English as "Kaitoh" rather than "Kaito".
Diend only has access to a single form by using the Diend KamenRide Card in the Diendriver and then shooting the Diendriver above him. In this form, Diend can move extremely fast when he personally fights rather then use his KamenRide cards through the use of the microwave-emitting Tesla Bands around his wrists. Decade also has Tesla Bands, but does not use them. Diend can also perform the Blue Strike (ブルーストライク, Burū Sutoraiku?)Rider Kick.
This form appears in Kamen Rider × Kamen Rider × Kamen Rider The Movie: Cho Den-O Trilogy; similar to Decade's Complete Form with the exceptions of movie based main antagonistic Riders being on his chest armor instead of the main or secondary riders. While Decade's is powered by the protagonist Heisei KamenRiders and their ultimate forms, Diend Complete Form is powered by the main antagonistic Kamen Riders of the Heisei Kamen Rider films (no Kamen Rider from a Den-O film is included):
Daiki transforms into Diend through the use of the Transformation Loading Gun Diendriver that functions likeDecade's Decadriver, placing a Ride Card inside it to activate it by firing. However, unlike Decade who transforms into another Kamen Rider, Diend'sKamenRide Cards enable him to summon other Kamen Riders to fight for him.
Unlike Decade who transforms into another Kamen Rider, Diend uses his KamenRide cards to summon another Kamen Riders. Diend is not limited to just the nine previous primary Kamen Riders, but has access to any Kamen Rider
Kamen Rider Diend : This standard card transforms Daiki into Kamen Rider Diend. Narutaki presents Daiki with a Diend KamenRide Card that will make Diend stronger for the sole purpose of destroying Decade. Unlike the original card, it has a yellow background instead of a white one.
Drake : Summons Kamen Rider Drake. First used in the World of Agito to fight the Grongi.
Delta : Summons Kamen Rider Delta. First used in the World of Agito to fight the Grongi.
Blade : Summons Kamen Rider Blade. First used in the World of Agito to fight the Lords.
Sasword : Summons Kamen Rider Sasword. First used in the World of Den-O to fight the Momotaros-possessed Yusuke.
Saga : Summons Kamen Rider Saga. First used in the World of Den-O to fight the Momotaros-possessed Yusuke.
Riotrooper : Normally summons three Riotroopers. First used in the World of Den-O to help Tsukasa and Momotaros fight the Alligator Imagin, then in the World of Kabuto to battle Kamen Rider Gatack. and uses it a third time in his world to battle the DarkRoaches. Diend summons five Riotroopers to fight Kamen Rider G Den-O in film Kamen Rider × Kamen Rider × Kamen Rider The Movie: Cho Den-O Trilogy.
Caucasus : Summons Kamen Rider Caucasus. First used to battle the Oni Rider Brothers, Caucasus is quickly possessed by Kintaros. This card was shown later on Diend's Complete Form.
G3 : Summons Kamen Rider G3. First used to battle the Oni Rider Brothers, G3 is quickly possessed byUrataros. In Kamen Rider Battle: Ganbaride Diend was able to summon G3's Complete Form - G3-X
Ouja. : Summons Kamen Rider Ouja. First used to battle the Oni Rider Brothers, Ouja is quickly possessed by Ryutaros. This card is also included with the DX Diendriver toy and also used by Diend in Kamen Rider Battle: Ganbaride and Kamen Rider: Climax Heroes
Ixa : Summons Kamen Rider Ixa. First used in the World of Kabuto to battle Kamen Rider Kabuto. When he is summoned he first says "Return that life you took to God!" .
Psyga : Summons Kamen Rider Psyga. First used in the World of Kabuto to battle Kamen Rider Kabuto. When he is summoned he first says "It's Show Time!" .
Den-O : Summons Kamen Rider Den-O. First used in the World of Hibiki. When he is summoned he first says "Here I Come!"
Scissors : Summons Kamen Rider Scissors with Strike Vent. First used in the World of Shinkenger to fight ShinkenGold.
Raia : Summons Kamen Rider Raia with Swing Vent. First used in the World of Shinkenger to fight ShinkenGold. Diend uses it again in the World of Decade to fight Ohja and Kick Hopper.
Ketaros : Summons Kamen Rider Ketaros. First used in the World of Black RX to fight Decade.
Hercus : Summons Kamen Rider Hercus. First used in the World of Black RX to fight Decade.
Femme : Summons Kamen Rider Femme. First used in the World of Black to fight Kamen Rider Black.
Black : Originally, this card belonged to Tsukasa. Unlike the rest of the Riders summoned by Diend, this summons the World of Black's Minami Kotaro, who then transforms to Kamen Rider Black.
Gai : Summons Kamen Rider Gai armed with Strike Vent. First used in the World of Decade to fight Ouja and Kick Hopper.
Punch Hopper : Summons Kamen Rider Punch Hopper. First used in the World of Decade to fight Ouja and Kick Hopper.
J : Summons Kamen Rider J in Jumbo Formation. Used in the World of Decade to fight King Dark.
Agito: Summons Kamen Rider Agito. First used in the World of Decade to fight Doctor Shinigami and the Dai-Shocker Soldiers in the 7-Eleven promotional campaign.
Black RX: Summons Kamen Rider Black RX. Used in the World of Decade to fight Doctor Shinigami and the Dai-Shocker Soldiers in the 7-Eleven promotional campaign.
Super-1: Summons Kamen Rider Super-1. Used in the World of Decade to fight Doctor Shinigami and the Dai-Shocker Soldiers in the 7-Eleven promotional campaign.
Zanki : Summons Kamen Rider Zanki. Used in the World of Amazon to fight Apollo Geist and Llumu Qhimil.
Ibuki : Summons Kamen Rider Ibuki. Used in the World of Amazon to fight Apollo Geist and Llumu Qhimil.
Todoroki : Summons Kamen Rider Todoroki. Although it is assumed that Diend uses it in the World of Blade to break up the fight between Decade and the BOARD Riders, it is not seen until it is used again in the World of Amazon to fight Apollo Geist and Llumu Qhimil.
G4: Summons Kamen Rider G4. Never used in show, but probably exists, because the card was shown on Diend's Complete Form
Orga: Summons Kamen Rider Orga. Never used in show, but probably exists, because the card was shown on Diend's Complete Form
Glaive: Summons Kamen Rider Glaive. Never used in show, but probably exists, because the card was shown on Diend's Complete Form
Arc: Summons Kamen Rider Arc. Never used in show, but probably exists, because the card was shown on Diend's Complete Form
Skull: Summons Kamen Rider Skull. Never used in show, but probably exists, because the card was shown on Diend's Complete Form. It is remains unknown whether that Daiki owns the card or owned by Tsukasa before he gave it to Shotaro Hidari during Movie War 2010 event.
Diend also has his array of Final FormRide Cards. Where as Decade activates the Heisei Riders' Final Formsby reaching his hands into their back, Diend activates them by shooting the Rider in the back, commenting beforehand "This will only hurt for a moment."
Kiva Arrow: Transforms Kiva into a large Kivat-like Bow with an arrow resembling Kiva's unsealed Hell'sGate leg.
Blade Blade: Transforms Blade into a large sword similar to the Blay Rouzer.
DenLiner: Daiki shows that he has this card, but he does not use it. When this card is taken by Decade, it is changed into the Momotaros Final FormRide Card.
Momotaros: Transforms Den-O into Momotaros.
Decadriver: In the film Kamen Rider Decade: All Riders vs. Dai-Shocker, this card allows Decade to transform into a giant version of the Decadriver called the Jumbo Decadriver . It is used to allow KamenRider J to transform into Kamen Rider Decade Complete Form Jumbo Formation.
These cards are Diend's most powerful attacks, used for finishing off enemies.
Diend: Diend performs the Dimension Shoot. Nine rings of cards appear before the Diendriver. Diend then sucks in any Riders summoned by his KamenRide cards before firing a shot from the Diendriver at the target, coming out as a green and black beam.
In Episode Yellow, Diend's Complete Forms Final Attack Ride is the Enhanced Dimension Shootwhich shoots out a gold-colored beam of energy.
Kiva: With the Kiva Arrow, Diend performs the Diend Fang.
Blade: With the Blade Blade, Diend performs the Diend Edge.
During the events of Episode Yellow: Treasure de End Pirates, Diend gets his own K-Touch which allows him to transform into Complete Form. It has one less button, as Diend's Complete Form Riders number only 8.