"Mushi-Uta" is a manga series set in a world where mysterious insect-like creatures known as "Mushi" exist. These Mushi attach themselves to humans, granting them supernatural abilities in exchange for feeding on their hosts' dreams and emotions. However, the Mushi eventually consume their hosts entirely, leading to their demise. The story revolves around a secret government organization called the Special Environmental Preservation Bureau (SEPB), which monitors and controls Mushi hosts, often referred to as "Mushi-shi" or "Dream Users."

The protagonist, Daisuke Kusuriya, is a high school student who becomes a Mushi host after encountering a Mushi known as the "Sleeping Beauty." This Mushi grants him the ability to heal others but at the cost of his own life force. Daisuke's life takes a dramatic turn when he meets Rina Tachibana, a girl who harbors a powerful Mushi called the "Fuyuhotaru" (Winter Firefly). Rina's Mushi allows her to manipulate fire, but it also makes her a target for the SEPB and other hostile Mushi hosts. Together, Daisuke and Rina navigate a dangerous world where they must confront the SEPB, rogue Mushi hosts, and the moral dilemmas of using their powers.

The narrative explores themes of sacrifice, survival, and the consequences of wielding power. Daisuke struggles with his desire to protect others while grappling with the inevitability of his own death. Rina, on the other hand, seeks to understand her past and the origins of her Mushi, which is tied to a tragic event in her childhood. The series also introduces other key characters, such as Shiika Anmoto, a former Mushi host who becomes an ally, and Aria, a mysterious girl with her own agenda.

As the story progresses, the SEPB's true motives are revealed, including their experiments to create artificial Mushi and their attempts to control or eliminate Mushi hosts. The conflict escalates as Daisuke and his allies uncover deeper secrets about the Mushi and their connection to humanity. The series balances action, emotional depth, and philosophical questions about the nature of dreams, desires, and the cost of power. Through its intricate plot and character development, "Mushi-Uta" presents a compelling exploration of a world where the line between humanity and monstrosity is blurred.