Baku meets Minami, who has become an agent, in a dream. Baku helps Minami with her mission to find a lost cat, but they are attacked by a Nightmare, and he wakes up. A "Black Case" has occurred in which Minami has grown a cat's tail. When Baku falls asleep again, he challenges the Nightmare to battle in order to save Minami, but...!

Minami is a CODE agent... Upon learning the truth, Baku is disappointed and furious, realizing that Minami had merely been "pretending to be family." In his dream, Minami is transformed into the Cat Nightmare once again. Baku transforms into Zeztz Catastrom and, despite knowing her true identity, attacks the Cat Nightmare...!?

"You will be eliminated by CODE..." After receiving this ruthless verdict from Zero, Baku infiltrates Zero's dream. Attacked by a mysterious black Zeztz, Baku is forced to confront a terrifying truth! Meanwhile, Sieg, plotting to use Nem, lures her into the Nightmare Prison. Terrified by countless Nightmares, Nem is cornered by Sieg...!?

Zero, his biological father, had been using his son, Baku, for Zeztz's sake. Unable to accept his own cruel fate, Baku is tormented by his inability to understand Zero’s true intentions. Will Baku be able to overcome this nightmare…!?

Sieg turns Nem’s nightmare into a prophetic vision, causing the Nightmare to manifest in the real world and attack civilians; witnessing the chaos, Baku uses his damaged Zeztz Driver and attempts to transform with a Capsem, but something goes wrong as he struggles to become Zeztz.

Revived, Baku enters the depths of Sieg’s psyche—driven by an obsession with Nem’s nightmares—and uncovers the truth behind his past; after identifying the Nightmare within him, Baku confronts Sieg once more, leading to a decisive battle between Zeztz and Dawn.

When Baku awoke from an ominous dream, the real world had been completely transformed. Determined to uncover the truth, Baku returns to the dream world, only to find that Nem was being targeted by Six. As Baku scrambles to protect Nem, Three appears and demonstrates a terrifying power...!?

After being saved by Nox, Baku is pressed to reveal the location of CODE's base, which he saw in a prophetic dream. It seems Nox intends to storm CODE's headquarters... After much internal struggle, Baku also resolves to destroy the activation device of Code: Somnia. Nox clashes with Three, while Baku faces off against Five and take back the world from CODE!

As development of the Zeztz Driver nears completion, Baku comes under attack from Nox, who has been manipulated by Three and transformed into a ruthless warrior. Despite fighting back with the Capsem, Baku finds himself increasingly overwhelmed by Nox’s relentless assault. Meanwhile, in the real world, Three senses a threat to his plans and forcibly awakens Zero in an effort to stop the Driver from being completed, setting the stage for a desperate battle on multiple fronts.

Determined to destroy CODE even at the cost of his own life, Baku tracks down the missing Nox by diving into his subconscious. There, he witnesses Nox awaken a new power through the Capsem and transform into Kamen Rider Nox. As Nox declares his intent to cast everything into darkness, he confronts Lord Three in a fierce showdown, setting the stage for a battle that could decide the fate of both worlds.

A new "Black Case" emerges, seemingly linked to the missing Capsem once used by Code: Somnia. Acting on Zero's orders, Baku sets out to recover it before the situation spirals out of control. His search leads him to Sieg, whose fused Nightmare has fully awakened. Suspecting Sieg of stealing the Capsem, Baku transforms into Zeztz and engages him in a fierce battle, unaware that an even greater threat may be lurking behind the incident.

A series of "black cases" has occurred in which people who have committed crimes in the real world have gone missing. It appears to be the work of the Punish Gore Nightmare, who metes out divine punishment to sinners. Even if they are sinners, this is going too far! Nox joins Baku in his attempt to stop the Nightmare's rampage. Facing their most formidable enemy, the two transform into Zeztz and Rider Nox!