Sokichi Narumi (鳴海 荘吉 Narumi Sōkichi) is Kamen Rider Skull (仮面ライダースカル Kamen Raidā Sukaru), he is also 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 Kumo Otoko) , 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, Sokichi 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 taught Shotaro about being a detective as well as acting somewhat like a father figure to him. Around Christmas, after scolding Shotaro for wearing his hat without permission as well as telling Shotaro to not wear it until his approval, 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. Even though Sokichi seemingly died, his will as a protector of Futo continues to live through Double as noted by Philip.
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 doesn't seem to know Shotaro, but regardless, praises him. He then takes his leave after telling Shotaro the way he wore his hat was proof of being a full man as well as telling him that they should meet again.
Kamen Rider Skull's final appearance is in Kamen Rider W Forever: A to Z/The Gaia Memories of Fate, where the ghost of Sokichi who transformed into Skull gives Shotaro his Lost Driver as well as helped him realize Philip`s feelings 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.
During Akiko's wedding, Sokichi appears for the final time in spirit, walking with his daughter down the aisle and entrusting her to Ryu.
Several years later, Sokichi would reappear through unknown means, rescuing a defeated Eternal on his SkullBoilder. before driving away with the unconscious Kamen Rider. Their whereabouts are currently unknown at this time.
A hard boiled person who helped the citizens of Futo as both a detective and as Skull, Sokichi lived and died while helping others. At a younger age, Sokichi was already a rather cheerful man with his partner Matsu while sometimes showing a comical and stubborn side. As well as helping Shroud through sheltering her, Sokichi still called Matsu his partner despite his betrayal and crimes later on. It seems the confrontation and death of Matsu combined with no longer being able to meet Akiko again has changed Sokichi though, as he seemingly became less cheerful and more cold.
Although he seemingly wasn't with Akiko much in her childhood, Sokichi clearly cared for her which was shown when he became motivated through talking with her on the phone. This fatherly side is also shown through his mentoring of Shotaro whom he acted both strictly and understandingly. He is quite forgiving towards others as he forgave not only Matsu, but Shotaro as well when he indirectly caused his own death. He was also the one who convinced Philip to make his own decisions right before his (Sokichi) death.
While mostly good, Sokichi was also somewhat the opposite of Shotaro as he mercilessly caused the Bat Dopant to die a painful death as well as allowed Bito to lie and turn himself to the police without a word. He also didn't say a word about Matsu's death but instead quietly walked away. Another difference was that Sokichi had a policy about using Gaia Memories which somewhat caused him to die whereas Shotaro uses them quite frequently as well as being proud to be W and Joker. Although Sokichi died, his will continues to live on through Shotaro and the others as he seemingly continues to support them through spirit.
- Height: 203cm
- Weight: 110kg
- Ability perimeters
- Punching power: 2 tons
- Kicking power: 3.5 tons
- Maximum jump height: 500m
- Maximum speed: 100m/8 seconds
Kamen Rider Skull Crystal (仮面ライダークリスタルスカル Kamen Raidā Sukaru Kurisutaru) is Skull's incomplete form. It differs from Kamen Rider Skull's standard form in that the helmet is iridescent and it lacks the S-shaped "crack". Skull Crystal is able to attack by releasing energy from his chest in the shape of a large purple skull that can bite opponents. This form is named after the crystal skulls.
- Height: 205cm
- Weight: 100kg
- Ability perimeters
- Punching power: 2 tons
- Kicking power: 6 tons
- Maximum jump height: 45m
- Maximum speed: 100m/6.3s
Through the use of the Lost Driver and Skull Memory, Sokichi transforms into Kamen Rider Skull. Skull is unique in that besides wearing a white tethered scarf he also wears a white fedora. It is revealed that he was the original user of the quote "Now, count your crimes!" (さあ、お前の罪を数えろ！ Sā, omae no tsumi o kazoero!), a quote now used by his successor. Skull's motif is that of a human skull and the letter S. Like Skull Rider, Skull appears to be a homeage to Skull Man, Shotaro Ishinomori's previous creation, who was adapted for the creation of Kamen Rider 1. Kamen Rider Skull's primary finisher is the long range shooting attack Skull Punisher (スカルパニッシャー Sukaru Panisshā), the Maximum Drive ability of his Skull Magnum. In Skull: Message to Double, Skull is shown to have a second Maximum Drive, known only as Finisher Kick (必殺キック Hissatsu Kikku), that involves releasing a giant energy skull from his chest, which stuns the opponent and knocks them back before rising into the air. Skull then puts the Skull Memory into the Maximum Drive Slot, jumps up, and does a roundhouse Rider Kick, which propels the energy skull toward the opponent, whom it bites down on. Kamen Rider Skull also appears as one of the Kamen Riders summoned by Kamen Rider Diend's Complete Form and his Gekijouban Card. In this appearance, his Maximum Drive attack is a generic Rider Kick, similar to Rider 1's famous somersault and kick attack, but with a purple swirling energy around Skull's right foot. In Ganbaride, the name of Skull's generic Rider Kick is Silhouette Kick (シルエットキック Shiruetto Kikku).