Sokichi Narumi

"Now, count up your sins."

- announcement before battle.

Kamen Rider Skull (仮面ライダースカル) is a Kamen Rider first appearing in Kamen Rider × Kamen Rider Double & Decade: Movie War 2010.

Background
Sokichi Narumi (鳴海 荘吉) was Shotaro's mentor (whom he refers to as "boss"), Akiko's father, and founder of the Narumi Detective Agency in Futo City. While working as a private investigator, he was partnered with a man, similar to his protege Shotaro Hidari's partner Philip, named Seiichiro Matsui (nicknamed Matsu) and had the personal policy of never getting clients in danger. He also provided his childhood friend Fumine Sonozaki (now Shroud) refuge after she was forced to leave her family and take up her new identity. Sokichi gets a job to protect a friend of his and Matsu's, Melissa, who is a singer. She receives a letter from a man calling himself "the Spider Man" (クモ男), which tells her to sing a specific song. The letter goes on to say that the Spider Man will rate the song on a scale of 1-100 and for every point below 100, he will kill an audience member. After confronting Melissa's agent at the concert, the Spider Man, revealed to actually be the Spider Dopant, attacks the crowd. He gives Melissa 100 points, and no one would be killed. However, Sokichi takes the opportunity to attack the Dopant armed with only the Stag Phone. A young Shotaro is in the audience, and comments in awe of how cool Sokichi is. After returning home, Soukichi talks to Shroud, who is working on the secret hangar (which then housed the SkullGarry). Shroud offers him the Skull Memory and Lost Driver when he asked her for suggestions on how to fight the Dopants. He rejected the gift outright due to wanting to keep his humanity intact.

Sokichi investigates further into Melissa's agent, and at the Yaguchi Talent Agency encounters the Spider Dopant again, along with the Bat Dopant and many Masquerade Dopants. Sokichi is almost killed by the Spider Dopant, but at the last second, Shroud arrives and tosses him the Lost Driver, the Skull Memory already inserted. The Driver attaches itself to Sokichi's waist, and he transforms into Skull Crystal against his will. Shroud notes that Skull is still incomplete, but Sokichi resumes his fight with the Spider Dopant and his horde of Masquerade Dopants nonetheless. During the fight, an energy sphere begins emerging from Skull's armor, but its appearance distracts Sokichi and gives the Dopants the upper hand. After receiving a call on the Stag Phone from Akiko, Sokichi gets the motivation to fight off the two Dopants. After seeing Yaguchi assumed to be the Spider Dopant, he was supplying Museum with test subjects, but killed by one of the Spider Bombs. Sokichi determines that the Spider Dopant's true identity is Matsu, thanks to noticing a quirk in his handwriting appear in a message the Dopant webbed on a wall. Sokichi confronts Matsu and learns his whole reason for becoming the Spider Dopant was because he was madly in love with Melissa, but she loved Sokichi. He implanted a Spider Bomb in Melissa, and tells Sokichi that the bombs activate when their host touches the one they love most. After infecting not only Sokichi, but most of Fuuto as well, Matsu departs as Spider Bombs explode all over Fuuto.

Sokichi runs after Matsu but is intercepted by the Gaia Memory Dealer, Eren Komori, who transforms into the Bat Dopant. Sokichi transforms into the complete Kamen Rider Skull, and fights the Bat Dopant. Instead of a Memory Break, Sokichi leaves Komori to die by leaving her trapped under a leaking gas tanker truck, which then explodes. He then goes to fight Matsu, and begins counting his sins: how he didn't see the darkness in Matsu's heart, how he hesitated to fight Matsu when the time came, and because of these sins, Fuuto suffered. He then tells Matsu to count his own sins, and the two fight once again. Sokichi ends the fight with his Maximum Drive, but because of the Memory's side effects, Matsu dies.

Despite his crimes, Sokichi still called Matsu his partner. Since the incident, Sokichi took the motto "Now, count your sins!" to heart so that nothing similar ever happens again. Furthermore, the Spider Bomb implanted in Sokichi did not fade after the Spider Memory's destruction. Knowing what would happen if he ever saw her again, Sokichi isolates himself from Akiko to ensure his daughter's safety. After this, Sokichi became involved in investigating cases involving Dopants that the police force could not handle, including the armored car robberies performed by the "Beastman".

Eventually taking Shotaro Hidari as his protege, Sokichi agrees to help Shroud stop the Museum by infiltrating a research facility known as the Gaia Tower with Shotaro in order to find the young man at its center. However, Sokichi is intercepted by several henchmen of Museum. Telling Shotaro to stay put with the suitcase he brought with them (which contained the Double Driver and all of Double's Memories), he defeats them with little effort. However, the men become Masquerade Dopants, and the Taboo Dopant appears. Having no choice, Sokichi transforms into Skull, much to Shotaro's awe. After dealing with the Dopants, Sokichi finds that Shotaro inadvertently sent the young man they were looking for to the crystal chamber used to create Memories at the top of the tower. Sokichi touches the chamber upon their arrival, and enters the Gaia Library, something the boy says only an impressive man could do. Sokichi offers him freedom to find atonement for his part in the creation of the Gaia Memories, naming him Philip after his favorite fictional character, Philip Marlowe. After Sokichi frees Philip from the Gaia Tower and begins to take both him and Shotaro out of the building, he is shot by several armed guards. As he dies, he gives his white fedora to Shotaro and asks Shotaro to become a man worthy of wearing it. It was after the Gaia Tower fell into ruins that Shotaro and Philip, spurred by his advice to continue in his place as Double, learn that Sokichi's body is nowhere to be found.

In Begins Night, Sokichi Narumi and Kamen Rider Skull are among the identities taken by the Dummy Dopant while pretending to be the Death Dopant in a scheme to assume the identities of Fuuto's upper class members, using Sokichi's form to drive Shotaro off from the case before he realizes the truth. However, Shotaro finally overcomes this and Double ultimately defeats the impostor Kamen Rider Skull. After the case is concluded in Movie War 2010, Tsukasa Kadoya uses a Kamen Rider Skull card he has acquired to summon an iteration of Sokichi Narumi from an alternate dimension, giving Shotaro closure. This Sokichi does not seem to know Shotaro but recognizes the very thing that the real Sokichi wanted of Shotaro: for him to become a true detective.

Kamen Rider Skull's final appearance is in Kamen Rider W Forever: A to Z/The Gaia Memories of Fate, where he gives Shotaro his Lost Driver before fading away as he takes his leave, enabling Shotaro to transform into Kamen Rider Joker. The Skull Memory is also one of the 26 T2 Gaia Memories in the film.

Lost Driver
The Lost Driver is Skull's transformation belt. Sokichi received this from Shroud to combat Dopants easier. It is similar in design to the Double Driver used by Double, except for having only one Memory slot.

Gaia Memories
Skull Memory: The Skull Memory also called the Skeleton Memory is the Gaia Memory used for the transformation into Kamen Rider Skull and for Maximum Drives. When placed in the Maximum Drive slot, it performs a Finisher Kick, and the Skull Memory can also be used in conjunction with his Skull Magnum.

Skull Magnum
The Skull Magnum is a firearm similar to the Trigger Magnum in Maximum Mode used by Double. It is gained through the power of the Skull Memory its Maximum Drive called the Skull Punisher which blasts the opponent with powerful rapidfire shots.

Memory Gadget
Skull, like Double, also used Memory Gadgets, supplied by Shroud, to combat the Dopant threat.
 * The Stag Phone (スタッグフォン) is the only existing Memory Gadget in 1999, used by Soukichi Narumi as his primary weapon prior to his becoming of Skull. The Stag Phone switches between Cell Phone Mode (携帯モード) and Stag Mode (スタッグモード) with the use of the Stag Memory (スタッグメモリ). When in Cell Phone Mode, it allows Kamen Rider Skull to summon the SkullGarry.

SkullBoilder
Skull also has a modified Honda CBR1000RR motorcycle similar to Double's HardBoilder, but all black in color and with half of the "W" symbol (which makes it the "S" symbol) painted silver, to represent Skull's Lost Driver. It is armed with a series of guns called the Universal Launchers (ユニバーサルランチャー).

SkullGarry
The SkullGarry (スカルギャリー) is a tank/garage that holds the SkullBoilder. It was created by Shroud and the vehicle later becomes Kamen Rider Double's RevolGarry after extensive redesigning. The SkullGarry only appears in the Kamen Rider Skull: Message for Double portion of Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie War Core.

Rider Cards

 * KamenRide: Skull: A Rider Card containing the power of Kamen Rider Skull possessed by Kamen Rider Decade. Unlike the others, it was sealed. Decade gave it to Shotaro Hidari, the left half of Kamen Rider Double. After he left a Soukichi Narumi from another world appeared through a dimensional wall and spoke to Shotaro.
 * A KamenRide: Skull card is also one of the eight cards used by Kamen Rider Diend Complete Form. It summons Kamen Rider Skull.

Other media appearances

 * Kamen Rider Skull briefly makes an appearance in Kamen Rider W episode 13 "The Radio Q/Targetted Princess". Sokichi Narumi makes an appearance in a flashback in episode 10 "The S Terror/The Great Detective's Daughter", as well as in a flashback in episode 31 "The B Carried on the Wind/The Beast Pursues".
 * During the encore at Koji Kikkawa's concert at the NHK Hall, Kikkawa appeared dressed up as Sokichi Narumi and performed the song "Big Sleep". At the same time, he was joined on stage by Kamen Rider Double.
 * Sokichi Narumi and Kamen Rider Skull are the main characters in the side-story presented in the "Nobody's Perfect" music video, a song credited to Narumi but sung by Koji Kikkawa. In the music video set during his life and prior to Philip's freeing, Narumi takes on a case of a kidnapping by the Museum of a young girl. He crosses paths with several Masquerade Dopants and the Terror Dopant, fighting the latter as Kamen Rider Skull.
 * Kamen Rider Skull appears as an Other Rider in the video game Kamen Rider Battride Wars.

Portrayal
Sokichi Narumi is portrayed by singer-songwriter Koji Kikkawa (吉川 晃司). Kikkawa also performs the song "Nobody's Perfect" under the name of his character. As Kamen Rider Skull, his suit actor was Eitoku (永徳). In Skull's appearance in Episode Yellow: Treasure de End Pirates, his suit actor was Riichi Seike (清家 利一).