Baku Yorozu is an invincible agent who uses his lucid dreaming ability to brilliantly rescue Nemu, a national celebrity, and complete difficult missions in his dreams. One night, Baku is suddenly attacked by a monster, the Nightmare. In his lucid dream, Baku fights against invincible foes, but for some reason, he is unable to defeat the Nightmare and runs away. Baku, cornered, encounters a mysterious person, who entrusts him with the Zeztz Driver and Capsems, and he transforms into Kamen Rider Zeztz!

In a dream, Baku somehow becomes a fugitive criminal. When he encounters the Bomb Nightmare, he transforms into Zeztz, but the Nightmare escapes. One night, Baku is suddenly summoned by Zero, who gives him an order to "infiltrate other people's dreams and prevent the Nightmare's nightmares before they happen." This means that he has to stop that bomber... Baku's mission to protect his "dream master" begins!

"To stop the nightmare, you must find the Mind's Door in the nightmare world." After receiving an order from Zero, Baku falls asleep and infiltrates Fujimi's nightmare to find the door to his mind. However, the Bomb Nightmare causes an explosion in front of Baku's eyes. If this continues, Fujimi's nightmare will become reality!? Baku transforms into Zeztz to save Fujimi and the world!

Baku dreams that he is guarding a VIP, the father of the bride, at a wedding rehearsal. Then a man appears and tries to steal from the bride, Miyuki. Baku's protection saves the day, but is he the dreamer of the Nightmare? On the day of the wedding, Baku, who is guarding the wedding in his dream, is confronted by a Nightmare who is after Miyuki. Baku transforms into Zeztz, and with the new powers he has gained from Zero, he challenges the Nightmare to a dogfight...!?

Why is the bride Miyuki the dreamer? Baku, who continues to gather information in the real world, comes in contact with Miyuki standing in front of a large tree in the park. He learns that Miyuki has a memory of the tree that could change her life. In the dream world, Baku finds Miyuki's Mind's Door and sees an unexpected scene behind the door. The Crow Nightmare appears again and attacks Miyuki and everyone else!

Baku is assigned a new mission: escape from prison. Baku tries to escape with Nem, Masumi Bijogi and Reiko, who are trapped in a prison nightmare, but their way is blocked by various traps. And what secret is hidden in the relationship between Nem and Bijogi? Nox appears in front of Baku and eerily says, "This is an inescapable prison of death." Will Baku be able to carry out his impregnable mission?

In a dream imprisoned within a prison, the dream master, Bijogi, took Nem and vanished. Puzzled by this bizarre behavior, Fujimi and Nasuka reveal a certain "cruel truth" to Baku. After learning everything, Baku returns to the dream world and takes on the mission anew to save Bijogi and Nem. But once again, Nox stands in Baku's way...!

Baku infiltrates the traditional restaurant "Royale Shirogane" in a dream to carry out a mission to destroy a biological weapon. Right before the wary Baku's eyes, Chef Shiomi, who had tasted the owner-chef Sannoh's dish, collapsed. Upon waking, Baku visits Sannoh's restaurant, where another unexplained food poisoning incident occurs. Could it be a biological weapon again? What is the true nature of the nightmare...!?

What is the nightmare Chef Sannoh desires? Baku finds a clue in the words of Shiomi and others in the real world, discovering Sannoh's third Mind's Door in a dream. Peering inside...! While Fujimi and the others scramble to stop the summit meeting, Baku transforms into Zeztz and collides with the Poison Nightmare. But then, Nox reappears once more...!?

Baku, tasked with the mission "Get back the national secret", infiltrates the home of art collector Atsumi in a dream. A theft occurs involving a famous painting from Atsumi's collection, and Baku suspects state secrets are hidden within that painting. However, as Baku pursues the culprit, Nox appears and warns him, "learning too much could destroy you." The next instant, Baku is struck by a blow from Nox's weapon...!?

The masterpiece stolen in the dream was corroded by the Nightmare. The national secret hidden within the painting would remain unrecovered if this continued... Baku was disheartened, but Zero rebukes him with an unusually stern tone. Baku once again transforms into Zeztz within the dream. As he grabbed the Wonder Capsem to protect Atsumi from the Mold Nightmare...!?

In his dream, Baku becomes an employee at the Space Center. His new mission: protect Earth from an approaching giant meteorite. Time until impact: 48 hours. Upon waking, Baku informs Fujimi and Nagumo of humanity's impending doom and springs into action. Returning to the dream world, Baku attempts to avert the asteroid collision alongside Nem. But there, Nox stands in their way. Before their eyes, Nox straps on a belt, loads a Capsem, and...!

After battling Nox Knight and acutely feeling his own powerlessness, Baku, having lost his confidence as an agent, is branded unfit by Zero. Still, a casual conversation with Seiya prompts him to reexamine himself. In a dream, he discovers Seiya's Mind's Door. Armed with a new Capsem, he confronts Nox!

Baku's new mission is to eliminate his enemy, Nox. Wandering through a black hole in his dream, Baku begins to retrace the nightmare he first saw as a child. Young Baku attends a cram school. Following his movements, the cram school instructor Nox appears! Shocked by this past encounter with Nox, Baku confronts him, desperate to recover his erased memories!