Here come the plot
At night in Tokyo, a man jumps from building to building, leaving sparkly sand as he moves. Momotaros, and the other Tarōs, are chasing after him because he is possessed by an Imagin. When they confront him, Momotaros thinks that he has seen the man before, and they see that he has a series of pink locks of hair, but when they attack he outwits them and they all hit each other. Ryotaro arrives, and this causes the Spider Imagin possessing the man to emerge, and then travel back in time. Ryotaro uses a Rider Ticket on the man, who has a blank expression on his face, and finds the past date to be November 22, 2008. The group goes to the DenLiner and become Kamen Rider Den-O Sword Form to fight the Spider Imagin in the past, easily defeating them after an Extreme Slash.
As Momotaros and the other Tarōs look around for the Rider Pass he tossed aside while performing the finishing attack, they see the man that was possessed earlier holding it, who explains he purposefully allowed the Spider Imagin to possess him so he could go back in time and so he could hijack the DenLiner. After shooting at the Tarōs with a strange gun, Momotaros remembers who this man is: "that robber guy" Daiki Kaito. Daiki escapes in the DenLiner, stranding Ryotaro and the Tarōs in 2008. On board, while holding the Owner and Naomi at gunpoint, the Owner explains that even though Daiki controls the DenLiner now, it will still go back to the date on the stolen Rider Pass.
When the DenLiner returns to November 22, 2008, Ryotaro and the Tarōs chase after it, until Ryotaro sees Daiki running off in another direction. He finds Daiki confronting his past self, who he shoots dead. However, the wound on the past Daiki disappears, allowing the past Daiki to get up and run away. The present Daiki shoots at his past self with the Diendriver more times, but the bullets disappear before impact. Before Daiki can attack again, a man suddenly appears from another point in time with a golden revolver trained on Daiki. He introduces himself as Reiji Kurosaki, a member of the G-Men and of the Time Police, and he holds out his badge which contains the artificial Imagin Eve. He has come to arrest Daiki for threatening to cause a time paradox in killing his past self. After mentioning something his mother once told him, he transforms into Kamen Rider G Den-O to arrest Daiki and remove him from history, if that is what he really wants.
As G Den-O turns his DenGasher into its Jutte Mode, Daiki transforms into Kamen Rider Diend, because he hates being deprived of his treasures, particularly his freedom. Diend appears to be no match for G Den-O's weaponry, and uses his Riotrooper Kamen Ride Card to hold G Den-O at bay. However, Eve is able to sense the Riotroopers movements and defeats them all. Diend prepares his Final Attack Ride Dimension Shoot, but G Den-O is able to counter with his "Perfect Weapon", forming a force field around himself and shooting at Diend with several red and blue lasers. The Riotroopers are destroyed, Diend is turned back into Daiki, and Daiki is arrested.
Ryotaro and the Tarōs are impressed, as G Den-O explains that because Eve is an artificial Imagin, he has infinite knowledge and is able to counter any attack. However, G Den-O soon shoots at Ryutaros, explaining that letting these Imagin survive and use the Rider Pass is threatening the timeline as well. He captures Momotaros, Kintaros, and Ryutaros, taking the Rider Pass and leaving Ryotaro behind. Urataros has managed to escape, and is following after the Daiki of the past who is breaking into the Kurosaki estate to steal a briefcase, and watches Daiki talk to and push aside a young boy who gets in his way. However, Urataros is found by Reiji Kurosaki who arrests him as well.
Back in the present time, Ryotaro is being given dinner from Airi, while he and Kohana try to figure out what Daiki was up to on November 22, 2008. Issē and Ozaki listen to the conversation, which reminds Ozaki of a theft that occurred at the Kurosaki estate on that date: someone broke in and stole the family's golden gun.
At the Time Police's jail, the Imagin try to talk their way out, while Daiki complains about the noise they are making. Kurosaki and several guards come by, and Daiki tells him that Kurosaki must be pleased that he has taken away Daiki's ultimate treasure, his freedom. Kurosaki replies, paraphrasing something that Urataros heard Daiki tell a young boy in the past, while Kurosaki trains his golden gun on Daiki again, its handle damaged. The Imagin are soon told that they will be put on trial, but the Owner appears and tries to get them out of trouble, only for the Owner to be arrested for harboring them. While he fights off the guards, Daiki manages to grab one of them, begging to be released if he promises to give up his life of crime. Kurosaki knows it is just a ploy and leaves with the guards. However, Daiki has managed to take the keys from the guard and frees himself, throwing the keys to the Imagin, but just out of reach.
On the DenLiner, which has been taken over by the Time Police, Naomi tells Kurosaki that Daiki has escaped. However, Kurosaki senses something off and aims his gun at Naomi, calling her Daiki. Daiki then takes of his Naomi disguise and two stare each other down. At the jail, Ryotaro and Kohana have been arrested as well, and put into the cell next to the Tarōs who are still trying to reach the keys. Ryotaro beckons for Momotaros to come closer, which Momotaros realizes what is being said as he possesses the boy, beating the guards, and letting everyone free. Ryotaro says they still have to get to the DenLiner, and the Owner gives him the Infinte Ticket, saying he has a meeting with the Station Master.
As Daiki is being forced off the DenLiner at gun point, Daiki manages to distract Kurosaki by saying Ryotaro and the others have escaped, as the DenLiner crew takes control of the DenLiner once more. Urataros steals back the Rider Pass, allowing them to return to November 22, 2008. Daiki has used the Diendriver to latch onto the back of the DenLiner, traveling with them. Kurosaki is angry that his prisoners have escaped, and Eve reminds him that their jdugement has already passed: total elimination. Diend manages to get to the DenLiner's cockpit and holds Den-O Sword Form at gunpoint, explaining that when he stole the gun the first time, he was distracted at examining his treasure by several letters hidden in the box, and he was shot at by several cops and he lost the gun which was damaged in the process. Ryotaro believes that he must want to steal it again, but not be caught, to which Daiki replies he prefers his treasures in mint condition.
Ryotaro, the Tarōs, and Daiki disembark from the DenLiner back in November 22, 2008, but are ambushed by G Den-O. Den-O fights back as several of his forms, including Ax Form who does not throw the Rider Pass aside when preparing his Dynamic Chop attack, and Urataros possesses Daiki to protect him from a gunshot, and transforms into Diend wielding a rod weapon to deflect bullets back. After Urataros leaves Diend, he uses the Invisible Attack Ride Card while Den-O Sword Form prepares an Extreme Slash again. The Extreme Slash is blocked by G Den-O's force field, but Diend has managed to get within the force field while invisible and shoots a point-blank blast from the Diendriver, leaving G Den-O temporarily incapacitated.
Daiki leaves to find his past self so he can get the gun before it is damaged. However, just before he can do anything Kurosaki appears. Eve prompts Kurosaki to get things over with. Before Daiki can get to his Diendriver once more, Kurosaki shoots him with the golden gun. The bullet goes through Daiki and hits the case the past Daiki is carrying, knocking it out of his hands, sending the papers within flying. The Daiki from the future catches the golden gun from the past, causing Kurosaki's gun to disappear from his hands. Daiki has gone back in time because he knew who Kurosaki was meant to become and he knew he was to be arrested so he could go back in time and steal the golden gun from the past so Kurosaki could never have it in the future. The papers in the briefcase were letters from Kurosaki's mother, telling him how much she loves him. Daiki tells Kurosaki that these should be his treasure, and gives them to him, leaving Kurosaki overcome with emotions.
Eve has been irritated that the final judgement has not been handed out and separates from Kurosaki's badge and transforms into G Den-O, saying that the Earth has no place for humans and their emotions. Everyone escapes from Eve as he starts attacking. Daiki runs into his past self, and as the two face off until G Den-O arrives. Both transform into Diend, and the one from the past holds him off as the one from the future escapes with the gold gun. Den-O arrives to fight G Den-O along with one of the Diends, and when a stray shot nearly hits Kurosaki, Diend saves him. Kurosaki thanks him by presenting Diend with his own K-Touch which he soon uses to become Diend Complete Form. He then uses the Attack Ride Gekijouban Card to summon Kamen Riders G4, Ryuga, Orga, Glaive, Kabuki, Caucasus, Arc, and Skull, and as a group, with Den-O Climax Form, destroy Kamen Rider G Den-O.
In the end, Daiki thanks the DenLiner crew for their help and heads off to the Hikari Photo Studio. Kurosaki goes to visit his mother at a flower shop she owns to talk to her, as they never did in the past. On the DenLiner, the Owner and the Station Master are having a contest where they are flicking balls of fried rice at plates at distances measured with the tape from Episode Red with the spoons from Episode Blue. Naomi serves everyone coffee, but Ryotaro's mug is missing, and he knows that Daiki must have taken it.