Kamen Rider Kuuga Rising Ultimate Form (ライジングアルティメットフォーム)

Kuuga's Rising Ultimate Form (ライジングアルティメットフォーム, Raijingu Arutimetto Fōmu)
 A form unique to Kamen Rider Decade is Kuuga's Rising Ultimate Form (ライジングアルティメットフォーム, Raijingu Arutimetto Fōmu). Much like Kuuga's other forms that were given a "Rising" upgrade within the original Kuuga, Rising Ultimate is an advanced version of Kuuga's Ultimate Form. In this form, Kuuga has a Rider Kick called the Rising Ultimate Kick (ライジングアルティメットキック, Raijingu Arutimetto Kikku). He also has the flaming Rider Punch called the Rising Ultimate Punch ライジングアルティメットキック, Raijingu Arutimetto Panchi) This form is accessed after Yuusuke has been attacked with the Stone of Earth by High Priestess Bishium, putting him under her control and unleashing all of Kuuga's potential. When Kuuga is freed of Bishium's control, the eyes change color from black to red. This form is used again in Decade: Final Chapter against Doras because of Decade's K-Touch.

Yuusuke Onodera (小野寺 ユウスケ Onodera Yuusuke^?) aka Ryouta Murai is Kamen Rider Kuuga in Kamen Rider Decade, basically a new installment of the character- an alternate version especially for the Decade series. He has a very self-confident and gullible child-like personality, a stark contrast to the original incarnation of Kuuga, Yuusuke Godai.
Yuusuke supports the police in fighting the Grongi and has feelings for Detective Ai Yashiro, as he fights to see her smile. When Yuusuke first discovered the Arcle Belt, he was warned of Decade's existence as the "devil" by Narutaki.
Yuusuke rarely engages in battle while journeying with Tsukasa. He does, however, act as a inspirational figure to the other Riders, as can be seen with his aiding of Wataru, as well as his actions in the other Riders' worlds.
 After killing the Grongi Me-Gyarido-Gi and Ra-Dorudo-Gu, Yuusuke answers Ai's call about another Grongi being spotted. After witnessing Decade defeat another Grongi, Ai and Yuusuke meet Tsukasa, who offers them his help as a policeman. Although Yuusuke seems to be annoyed by this, Tsukasa demonstrates his intellect and baits out two Grongi. Yuusuke recognizes Tsukasa transforming into Decade, the man who will defeat all the riders, and attacks him, but their battle is interrupted by Kick Hopper and Punch Hopper appearing due to a dimensional rift.

After the battle, Tsukasa goes off to a fight a revived N-Gamio-Zeda who is terrorizing the city by converting humans into Grongi using his miasma. Yuusuke saves Ai from the miasma, but is afraid to fight because she is dying. Her words are able to convince him otherwise, and Yuusuke, along with Tsukasa, defeats Gamio. However, upon his return, Yuusuke finds that Ai has died. Yuusuke promises to go on fighting, in order to protect everyone else's smile.
But after visiting Ai's tombstone to pay his respects, Yuusuke meets Kivala who brings him to Castle Doran in Kiva's World, where Yuusuke offers his aid to the Fangire King Wataru before joining Tsukasa's group as a resident of Hikari Photo Studio.
However during the Rider War, though his world is destroyed, Yusuke still exists due to his traveling of the Nine Worlds. Even though he is destroyed by Decade in The Last Story, he and his world are restored, allowing him to aid in reviving Decade and defeating the newly formed Super Shocker once and for all.