"Yumeria" centers around Tomokazu Mikuri, a high school student with a vivid imagination and a penchant for daydreaming. His life takes an unexpected turn when he begins experiencing strange dreams featuring a mysterious girl named Mone. These dreams blur the line between reality and fantasy, as Mone appears to Tomokazu in the waking world, claiming to be a manifestation of his subconscious desires. She introduces him to a surreal dream dimension called Yumeria, where imagination shapes reality.

In Yumeria, Tomokazu encounters a group of girls known as the "Dreamers," each representing a different aspect of his personality or desires. These include Neneko, a cheerful and energetic girl; Nanase, a calm and intelligent figure; and Koyomi, a shy and reserved character. Together, they navigate the dream world, which is governed by a system of rules and challenges tied to Tomokazu's subconscious. The Dreamers must work together to overcome obstacles and protect Yumeria from threats that arise from Tomokazu's inner conflicts and fears.

As the story progresses, Tomokazu's connection to Yumeria deepens, and he begins to uncover the true nature of the dream world and its ties to his own psyche. The narrative explores themes of self-discovery, the power of imagination, and the interplay between dreams and reality. The interactions between Tomokazu and the Dreamers reveal layers of his personality, as well as the complexities of their roles in his subconscious.

The series balances lighthearted moments with more introspective sequences, blending comedy, fantasy, and psychological elements. The dynamics between the characters drive the plot forward, as Tomokazu learns to confront his fears and desires while navigating the challenges of both his dream world and his everyday life. The resolution of the story ties together the threads of Tomokazu's journey, offering a conclusion that reflects his growth and the resolution of his inner conflicts.