Kouta earns the name "Armored Rider Gaim" as he decides to help Team Gaim as an official member in Yuya's stead. He finds five more Armored Riders appearing in Zawame with his Team Gaim team mate Mitsuzane becoming their group's primary Armored Rider Ryugen so he wouldn't focus his life around them. Learning the Inves' home is Helheim Forest, Kouta and Mitsuzane learn Sid is working with the Yggdrasill Corporation in an experiment involving the Armored Riders. Though the majority of the company believes his use to them is over, he finds himself receiving an Energy Lock Seed and a Genesis Core from DJ Sagara. Due to his status as a Beat Rider, he is unable to find a job until the Beat Riders' public reputation restored. Kouta is stopped in his efforts to stop Yggdrasil's goals by Takatora who proceeds to break the boy's spirit by revealing that the first Inves he killed was actually Yuya.
DJ Sagara approaches him and tells him his new purpose should be in destroying the rules the Yggdrasill Corporation is following in order to change the world for the better, rather than allow them to cull humanity. DJ Sagara creates the Kachidoki Lock Seed and gives it to Kouta. He later decides that he has to tell Mai the truth about Helheim Forest, including Yuya's fate, and after this point Mitsuzane betrays him, and nearly kills him in Helheim Forest, with only Baron saving him. After helping Zangetsu Shin save the Yggdrasill research camp from the Overlord Demushu, Kouta and Takatora join forces to stop the Overlords, believing they are key to ending the threat of Helheim, unaware that Ryoma plans on eliminating them for being in the way of his plans. Kouta then finally gets a job at Drupers, but only after his sister is downsized.
As Kamen Rider Gaim, he can wear Arms Changes by using different Lock Seeds in the Sengoku Driver, while gaining access to an Arms Weapon. His main form as Gaim is Orange Arms, which gives him access to the Daidaimaru sword. His finishing moves are the Burai Kick, the Daidai Itto with the Daidaimaru, and the Naginata Musou Slicer when he combines the Musou Saber and Daidaimaru into a naginata.