"D_Cide Traumerei the Animation" is a supernatural action series that intertwines mystery, psychological elements, and intense battles. The story centers around Ryuuhei Kiba, a high school student who becomes entangled in a hidden world of supernatural phenomena after encountering a mysterious girl named Sumeragi. Sumeragi reveals that Ryuuhei possesses a unique ability to enter a dreamlike dimension known as the "Traumerei," where individuals confront their deepest fears and desires manifested as monstrous entities called "Nightmares."

As Ryuuhei navigates this surreal realm, he discovers that he is not alone in his ability. Other individuals, known as "Dreamers," also possess the power to enter the Traumerei and combat Nightmares. These Dreamers are part of an organization called "D_Cide," which seeks to protect the real world from the encroaching threats of the Traumerei. Ryuuhei joins forces with fellow Dreamers, including the enigmatic Sumeragi, the stoic and skilled fighter Shougo, and the cheerful yet determined Akira. Together, they face increasingly dangerous Nightmares, each tied to the psychological traumas and unresolved emotions of their creators.

The narrative delves into the personal struggles of the characters, exploring themes of guilt, loss, and redemption. Ryuuhei's journey is particularly central, as he grapples with his own traumatic past and the responsibility of wielding his newfound powers. The series balances episodic battles against Nightmares with an overarching mystery surrounding the origins of the Traumerei and the true nature of D_Cide. As the story progresses, alliances are tested, secrets are uncovered, and the line between reality and the dream world becomes increasingly blurred.

The plot builds toward a climactic confrontation with a powerful entity that threatens to merge the Traumerei with the real world, endangering both dimensions. The characters must confront their inner demons and unite their strengths to prevent catastrophe. Through its blend of psychological depth, supernatural intrigue, and high-stakes action, "D_Cide Traumerei the Animation" offers a compelling exploration of the human psyche and the consequences of unresolved trauma.