Icon-w.png This article is about a/an transformation device in Kamen Rider W.

"(Memory) (Music)"
―Transformation announcement[src]

"(Memory) Maximum Drive!"
―Finisher announcement[src]

The Transformation Belt Lost Driver (変身ベルト ロストドライバー Henshin Beruto Rosuto Doraibā) is a 2nd Generation Memory Driver used by Sokichi Narumi, Katsumi Daido, and Shotaro Hidari to transform into Kamen Riders Skull, Eternal, and Joker respectively.


Due to using refined Gaia Memories that retain their form rather than be absorbed into the user's body, the user is completely shielded from its corrupting effects. This comes at the cost of the Gaia Memory's power being further weakened except for during a Maximum Drive. As it is a prototype that was later developed into the Double Driver, forms accessed with T1 Gaia Memories are extremely weak, though the user's personal experience may mitigate this as shown with Shotaro Hidari's fights after Philip's disappearance.

Two more Lost Drivers also existed. One, shown to be in the possession of the NEVER organization leader, Katsumi Daido, which he took from Jun Kazu of Foundation X. The other, given to Philip by Shroud in order to fight Zoo and Zebra Dopants as Kamen Rider Cyclone before he gave it to Shotaro after he sacrificed himself to save Wakana from the Gaia Impact.


The Lost Driver was an early attempt by Shroud to further refine the power of the Gaia Memories, after the success of the Gaia Driver. The first known Lost Driver was given to Sokichi Narumi following by Shroud following her escape from the Museum, though he initially refused it on the principle of fighting with his own strength. Sokichi eventually accepted the gift and used it in tandem with the Skull Memory to transform into Kamen Rider Skull. This Driver disappeared along with Sokichi following Phillip's liberation from the Gaia Tower.

The Dummy Dopant would later use the Dummy Gaia Memory to impersonate Sokichi, including replicating his Lost Driver, during the events of Begins Night. Even later, Sokichi's ghost seemingly appeared in front of Shotaro during the events of Kamen Rider W Forever: A to Z/The Gaia Memories of Fate, leaving his Lost Driver to his former protege. Shotaro used the Lost Driver along with the T2 Joker Memory to become Kamen Rider Joker to battle NEVER, though the Driver was seemingly lost before the end of the conflict.

Another identical Lost Driver was used by Jun Kazu and Katsumi Daido to become Kamen Rider Eternal, using both the original and T2 Eternal Memories, though this one was lost following Daido's destruction. After the destruction of the Museum, Shotaro discovers another Lost Driver left behind for him by Phillip, allowing him to continue protecting Futo using his own power. Despite Phillip's return from the True Gaia Memory a year later, Shotaro still carries the Lost Driver with him should he be forced to fight by himself.



By inserting a Gaia Memory into the Memory Slot (メモリスロット Memori Surotto) on the belt buckle, a user can transform into a Kamen Rider.

The transformation into a Kamen Rider will be canceled if a Gaia Memory is removed and not re-inserted for a certain amount of time.


Another slot on the right side of the Lost Driver is called the Maximum Slot (マキシマムスロット Makishimamu Surotto). When a Memory is placed in the Maximum Slot, a Kamen Rider can use a Maximum Drive (マキシマムドライブ Makishimamu Doraibu) finisher attack.

Users (chronological order)

User Kamen Rider Episode Obtained Episode Destroyed Description
Sokichi Narumi
Kamen Rider Skull
Skull: Message for W N/A The Skull Lost Driver was given to Sokichi Narumi by Shroud to aid him in his battle against Museum. She may have stolen it from Museum, as hinted by Saeko's reaction to Sokichi using it. After Philip hid the Lost Driver without telling Shotaro, Sokichi's spirit appeared and guided Shotaro to its location.
Father Roberto Shijima (As the appearance of Sokichi Narumi)
Kamen Rider Skull
W: Begins Night N/A As the Dummy Dopant, the user can assume any form he wishes. While assuming Sokichi's form, he can also manifest the Lost Driver and Skull Memory automatically, as he uses Skull's form to discourage Shotaro's interference.
Jun Kazu
Kamen Rider Eternal
Kamen Rider W Returns: Kamen Rider Eternal N/A Jun Kazu was given a Lost Driver and the T1 Eternal Memory from Foundation X, which he used to become Kamen Rider Eternal. However, he was not compatible with the Gaia Memory, so he could only access Eternal's Red Flare Form.

After Jun Kazu was killed by Katsumi Daido, his Lost Driver and Gaia Memory were taken by Daido, who became the second Kamen Rider Eternal.

Katsumi Daido
Kamen Rider Eternal
Kamen Rider W Returns: Kamen Rider Eternal Kamen Rider W Forever: A to Z/The Gaia Memories of Fate Daido took Jun Kazu's Lost Driver and T1 Eternal Gaia Memory after killing him and used them to become Kamen Rider Eternal. He later swapped out the T1 Eternal Gaia Memory for its T2 version.

Daido's Lost Driver was presumably destroyed when he was defeated by Kamen Rider Double at the top of Futo Tower.

Kamen Rider Cyclone
Kamen Rider W: ~The One Who Continues After Z~ N/A When Shotaro had fallen sick and was not able to fight, Shroud gave Philip a Lost Driver to use with his Cyclone Gaia Memory and become Kamen Rider Cyclone. After Shotaro recovers, Philip hides the Lost Driver, intending to not use it again.

After sacrificing his physical body to save Wakana, Philip gives his Lost Driver to Shotaro, who had lost his own, in order for him to become Kamen Rider Joker once again.

Shotaro Hidari
Kamen Rider Joker
Kamen Rider W Forever: A to Z/The Gaia Memories of Fate

The Abandoned U/Eternal Partners

N/A Shotaro was given Sokichi Narumi's Lost Driver by the latter's spirit, which he used with the T2 Joker Gaia Memory that he found to become Kamen Rider Joker. He lost this Driver soon after, however, when he was defeated by Kamen Rider Eternal.

Later, Philip gives his own Lost Driver to Shotaro after he had sacrificed his physical body, enabling Shotaro to become Kamen Rider Joker again with his T1 Joker Gaia Memory.

Kamen Riders


  • The Lost Driver is simply a standard Double Driver with the right half of its terminals removed. Nothing replaces the missing terminal, leaving it conspicuously empty.
    • It is possible to modify a toy version of the Double Driver by removing its right terminal to create a Lost Driver. An actual Lost Driver toy was released to coincide with the second film, with no changes besides the aforementioned missing right terminal and only including the Skull and Eternal memories. Either of these can be used with the Joker memory, although the Joker Memory included with the Double Driver toy is specifically timed to sound off after the left side memory, resulting in a noticeable delay after activation. The T2 Joker Memory toy released as a promotional item for second film does not share this issue.
  • It is unknown if the term "Lost" prefix has any particular meaning to the development of the Gaia Memory, as the only known applicable instance was the fact Shroud stole it from the Museum following her escape.


Narumi Detective Agency
Shotaro Hidari - Philip - Akiko Narumi - Sokichi Narumi† - Tokime
Memory Drivers
Double Driver - Accel Driver - Lost Driver
Gaia Memory-related
Gaia Memories - Memory Gadgets - Fang Memory - Xtreme Memory - Trial Memory - Gaia Memory Enhancing Adapter
Metal Shaft - Trigger Magnum - Engine Blade - Skull Magnum - Prism Bicker - Eternal Edge - Shroud Magnum
RevolGarry - HardBoilder - Gunner A - Diablossa - SkullBoilder - SkullGarry - HardMammother
The Fuuto Irregulars
Santa-chan - Watcherman- Queen & Elizabeth - Isamu Bito
Futo Police Department
Ryu Terui - Mikio Jinno - Shun Makura
Museum and the Dopants
Foundation X
The Sonozaki Family: Terror - Claydoll - Taboo/R Nasca - Nasca - Smilodon - Masquerade Dopants
Dopants: Magma Dopant - T-Rex Dopant - Money Dopant - Anomalocaris Dopant - Cockroach Dopant - Sweets Dopant - Virus Dopant - Violence Dopant - Arms Dopant - Bird Dopant - Ice Age Dopant - Triceratops Dopant - Liar Dopant - Puppeteer Dopant - Invisible Dopant - Nightmare Dopant - Beast Dopant - Zone Dopant - Yesterday Dopant - Quetzalcoatlus Dopant - Gene Dopant - Jewel Dopant - Old Dopant - Utopia Dopant - Energy Dopant
Movie Exclusive Villains: Dummy Dopant - Heat Dopant - Trigger Dopant - Metal Dopant - Luna Dopant - Cyclone Dopant - Bat Dopant - Spider Dopant - Kamen Rider Eternal - Commander Dopant - Eyes Dopant
Novel-Exclusive Villains (The One Who Continues After Z): Zoo Dopant - Zero Dopant - Queen Bee Dopant - Flower Dopant - Elephant Dopant - Dolphin Dopant - Salamander Dopant - Fish Dopant - Bird Dopant - Ape Dopant - Bee Dopants
Manga Exclusive Villains (Futo Detective): Road Dopant - Aurora Dopant - Meganeura Dopant -Brachiosaurus Dopant - Scream Dopant - Alcohol Dopant - Puzzle Dopant - Reactor Dopant - Antlion Dopant - Owl Dopant - Trash Dopant - Caracal Dopant - Toadstool Dopant
Yukiji Bando - Kazuha - Hideo - Mamoru Nikaido - Sabu
Katsumi Daido - Maria S. Cranberry - Reika Hanehara - Kyosui Izumi - Gozo Domoto - Ken Ashihara
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