Wataru (ワタル) is the resident Kamen Rider and the current Fangire King of the World of Kiva in Kamen Rider Decade.
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 Kamen Raidā Kiba) with the aid of Kivat-bat the 3rd. Referred to as the Prince (王子 Ōji) 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.
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.
Unlike the original Wataru who was humble, polite and mature, this Wataru was (initially) an immature, spoiled brat who had trouble respecting his elders. He was also quite cocky of his status thus making his personality more resembling towards Taiga. Like Taiga however, this Wataru was actually good deep down and tried to help others as the ruler of Fangires. Although he also did some questionable acts, this Wataru also did the right thing in the end (again like Taiga) as Kiva.
- Rider Height: 200cm
- Rider Weight: 92kg
- Ability Perimeters
- Punching Power: 6 ton
- Kicking Power: 8 tons
- Darkness Moon Break: 30 tons
- Max Jump Height: 85m
- Maximum Running Speed: 100m/6.5s
- Rider Height: 210cm
- Rider Weight: 100kg
- Ability Perimeters
- Punching Power: 18 tons
- Kicking Power: 32 tons
- Max Jump Height: 180m
- Maximum Running Speed: 100m/3s
Emperor Form (エンペラーフォーム Enperā Fōmu) is the true form of Kiva, referred to as the Golden Kiva (黄金のキバ Ōgon no Kiba) 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.
Kamen Rider Decade's Final Form Ride allows Kiva to change into the Kiva Arrow (キバアロー Kiba Arō). 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.
- Thanks to the Beetle Fangire, this Kiva has lost a large portion of his powers, since his own Arm Monsters had died by being absorbed by the Fangire.