Scott

"He believes... in the law. Despite that, he believes! You gave up! You lost to your own weakness... and forsook the law. But Wataru... fights for those who believe. That is what a king is! The qualification of a King!"

- Tsukasa talking about Wataru to Beetle Fangire

Scott is the resident Kamen Rider of the World of Vampire King in Kamen Rider DCD.

Wataru
He is a twelve-year-old half-Fangire boy, having the ability to transform into Kamen Rider Kiva (仮面ライダーキバ) with the aid of Kivat-bat the 3rd. Referred to as the Prince (王子) by his servants, Wataru is reluctant to claim the title of King (キング) of the Fangires. He finds the overseeing of the ceasefire between humans and Fangires a very troublesome and unnerving task.

Biography
Wataru first meets Tsukasa and Natsumi at Kurenai Manor where he is playing his violin. Later during a misunderstanding, Wataru transforms into Kiva to fight Decade, who he believes is the devil. Yusuke arrives and clears up the misunderstanding, offering his aid to Wataru and his task of serving as King. The next day, Wataru is confronted by the Beetle Fangire who intends to become the new King. The Beetle Fangire successfully claims Kivat as his own in the ensuing battle and proceeds to absorb the Arms Monsters into his Fangire armor, allowing him to become Kiva DoGaBaKi Form. After listening to Tsukasa make a speech about his ideals for the coexistence of humans and Fangire, Wataru takes back the power of Kiva, teaming with Decade to fight the Beetle Fangire. With a combination attack of Decade's Dimension Kick and Kiva's Wake Up (Darkness Moon Break), the Riders defeat the Beetle Fangire, who is later revealed to be Wataru's father, the former King.

He later appears in the World of the Rider War as his reality is absorbed into it. Leading the Riders of his world, Wataru refuses to listen to Tsukasa and Yusuke in uniting all Riders to defeat Dai-Shocker and stop the convergence of the worlds, while in grief over IXA's death. He even went so far to allow the Queen of the Fangires, Yuki, to marry Apollo Geist for the World of Kiva to have an advantage over the other A.R. Worlds, but later changes his mind when the Fangire betrayed them to Dai-Shocker. After defeating Super Apollo Geist, the convergence of the worlds continues and the World of Kiva and Wataru disappear along with the World of Hibiki and Asumu after the destruction of Super Apollo Geist by Decade and Diend.

However, in Kamen Rider × Kamen Rider W &amp; Decade: Movie War 2010, he is resurrected after Tsukasa has been killed by Kamen Rider Kiva-la. He later appears alongside the Riders of the Nine Worlds to revive Tsukasa and help him battle Super Shocker, assuming Emperor Form with the help of Decade's K-Touch and later uses Castle Doran to fight the Super Crisis Fortress.

Later appearances
Movie War 2010 currently remains the last appearance of Wataru. The Kiva that appears in OOO, Den-O, All Riders: Let's Go Kamen Riders and Kamen Rider × Super Sentai: Super Hero Taisen is the original Kiva, Scott Harker.

Forms
Just like the original Kamen Rider Kiva had various forms into which he could change into for different powers and specialties, the Kiva appearing in Decade has this same ability. The forms Wataru has transformed into are Kiva Form (キバフォーム), Garulu Form (ガルルフォーム), Basshaa Form (バッシャーフォーム), Dogga Form (ドッガフォーム). Kamen Rider Decade's Final Form Ride allows Kiva to change into the Kiva Arrow (キバアロー).

Kiva
"Gabu!"

- Kivat's transformation announcement

Kiva Form (キバフォーム) is Kiva's default form, accessed through a bite from Kivat, who status determines Kiva's ability in a battle. He is able to see in the dark with his visor called the Omnilens (オムニレンズ). In this form, Kiva can use any of the Fuestles, with the Wake Up Fuestle to open up the Catena Chains on his right leg known as the Hell's Gate (ヘルズゲート) made of Lucifer Metal (ルシファーメタル) so Kiva can use his Darkness Moon Break (ダークネスムーンブレイク) attack. The kick has an impact of 30,000 kg., enough to leave a crater in the shape of a bat's wings (Kiva's insignia) on any surface upon contact; the glass body of a Fangire shatters almost instantly. Kiva can also perform a stronger variation of the Darkness Moon Break when engulfed in Castle Doran's fire. When the Darkness Moon Break is performed, day turns into night and a crescent moon appears in the sky.
 * Rider height: 200 cm.
 * Rider weight: 98 kg.
 * Ability parameters
 * Punching power: 6 tons
 * Normal kicking power: 8 tons
 * Darkness Moon Break: 30 tons
 * Maximum jump height: 85 meters
 * Maximum running speed: 100 meters per 6.5 seconds

In Kamen Rider Battle: Ganbaride, Kiva is able to perform the Batty Punch, which involves Kiva jumping into the air and striking the opponent with a superman punch.

Garulu
Garulu Form (ガルルフォーム) is Kiva's form accessed from being energized by the Demon Beast-Sword Garulu Saber. In this form, the Omnilens and Kiva's chest/left arm armor turn a shade of blue called Garulu Cobalt (ガルルコバルト) which places Kiva under the influence of Garulu. This form's power is linked to the phases of the moon, and is at its peak when the moon is naturally full. The Garulu Form is capable of unleashing a blast of sound, has increased speed and cunning due to the form's animalistic ferocity and is able to perform the Garulu Howling Slash. When it is performed, day turns to night and a full moon appears in the sky, as it references a human's transformation into a werewolf.
 * Rider height: 200 cm.
 * Rider weight: 90 kg.
 * Ability parameters
 * Punching power: 5 tons
 * Kicking power: 9 tons
 * Maximum jump height: 40 meters
 * Maximum running speed: 100 meters per 1.5 seconds

Its motif is that of a Werewolf (狼男).

In Kamen Rider Battle: Ganbaride, Kiva in Garulu Form is able to perform the Wolfen Full Moon - a powerful blow from the Garulu Saber using the force of Lunar energy.

Basshaa
Basshaa Form (バッシャーフォーム) is Kiva's form accessed from the Basshaa Fuestle and granting him access to the Demon Sea Gun Basshaa Magnum. In this form, the Omnilens and Kiva's chest/right arm armor turn a shade of green called Basshaa Emerald (バッシャーエメラルド) which places Kiva under the influence of Basshaa. While in this state, Kiva loses most of his strength and agility, but gains a mastery of long range combat and is able to analyze an opponent's weak point to target with accurate marksmanship. Basshaa Form can also manipulate water, able to create rain as well as a pool of water necessary to perform the Basshaa Aqua Tornado. When it is performed, day turns to night and a half moon forms in the sky, as it references the change ebb and flow of the tides during its phase.
 * Rider height: 200 cm.
 * Rider weight: 92 kg.
 * Ability parameters
 * Punching power: 3 tons
 * Kicking power: 3 tons
 * Maximum jump height: 20 meters
 * Maximum running speed: 100 meters per 6 seconds.
 * Maximum swimming speed: 162 kt.

Its motif is that of the Gill-man (半魚人).

In Kamen Rider Battle: Ganbaride, Kiva in Basshaa Form is able to perform the Basshaa Finger - A quick pull on the Basshaa Magnum to launch fast and powerful water projectiles.

Dogga
Dogga Form (ドッガフォーム) is Kiva's form accessed from the Dogga Fuestle and granting him access to the massive Demon Iron Hammer Dogga Hammer. In this form, Kiva's entire upper body gains bulky armor and the Omnilens turn a shade of violet called Dogga Purple (ドッガパープル), placing Kiva under Dogga's influence. In this form, Kiva loses most of his speed but gains unbelievable strength, able to overpower a Fangire easily. Dogga Form is able to manipulate electricity, using it as part of his finisher, the Dogga Thunder Slap. The Dogga Hammer can see through the invisibility of Fangires. When it is performed, day turns to night while a hazy moon and thunderbolt form in the sky, the latter referencing its motif of Frankenstein's Monster (フランケンシュタインの人造人間) and how it was brought to life.
 * Rider height: 200 cm.
 * Rider weight: 150 kg.
 * Ability parameters
 * Punching power: 15 tons
 * Dogga Thunder Slap: 30 tons
 * Kicking power: 4 tons
 * Maximum jump height: 10 meteres
 * Maximum running speed: 100 meters per 10 seconds

In Kamen Rider Battle: Ganbaride, Kiva in Dogga Form is able to perform the Armor Hammer - A powerful strike from Dogga Kiva's heavy arm.

Emperor
"Henshin!"

- Tatsulot's transformation announcement

Emperor Form (エンペラーフォーム) is the true form of Kiva, referred to as the Golden Kiva (黄金のキバ) and the most powerful form at Wataru's disposal. This fifth form was only accessed with Tsukasa's K-Touch in The Final Chapter. With this form, Kiva can destroy both the body and the soul of a Fangire.
 * Rider height: 210 cm.
 * Rider weight: 100 kg.
 * Ability perimeters
 * Punching power: 18 tons
 * Normal kicking power: 32 tons
 * Emperor Moon Break 150 tons
 * Maximum jump height: 180 meters
 * Maximum running speed: 100 meters per 3.0 seconds

Final Form Ride
Kamen Rider Decade's Final Form Ride allows Kiva to change into the Kiva Arrow (キバアロー). Once the Final Attack Ride Card is in, the bow can be pulled back, getting the Hell's Gate to open up for the Decade Fang attack.