"Monmon" is a manga series that explores themes of grief, healing, and the supernatural through the lens of a young girl's journey. The protagonist, Monmon, is a child who loses her mother in a tragic accident. Struggling to cope with her overwhelming sorrow, she begins to see strange, otherworldly creatures that others cannot perceive. These beings, known as "Mushi," are ethereal and mysterious, often embodying the emotions and unresolved issues of the living. Monmon's ability to see them draws her into a hidden world where the boundaries between life and death blur.

As Monmon navigates this surreal landscape, she encounters a variety of characters who are also connected to the Mushi. Among them is a enigmatic man named Ginko, who serves as a guide and mentor. Ginko is a "Mushi-shi," a specialist who studies and deals with the Mushi, helping those affected by their presence. Through Ginko, Monmon learns more about the nature of the Mushi and their impact on the human world. The series delves into episodic stories, each focusing on different individuals and their encounters with the Mushi, while gradually revealing Monmon's personal growth and her evolving understanding of loss and acceptance.

The narrative is structured around Monmon's interactions with both the Mushi and the people she meets, highlighting the interconnectedness of life, death, and emotion. The Mushi themselves are portrayed as neither inherently good nor evil, but rather as forces of nature that reflect the complexities of human experience. Monmon's journey is one of self-discovery, as she learns to confront her grief and find meaning in her mother's passing. The series balances moments of melancholy with a sense of wonder, creating a poignant exploration of the human condition through its supernatural framework.