Guren is a central figure in Shonen Onmyouji, known primarily as the most powerful of the twelve shikigami, or Shinshou, bound to the legendary onmyouji Abe no Seimei. His existence is defined by a duality of form and nature; he possesses multiple names that reflect different aspects of his being. Originally known as Touda, the name representing his raw, untamed identity as a fire demon, he was later given the name Guren by Seimei. In his most unassuming form, he appears as Mokkun, a small, white, dog-like or fox-like creature who is talkative, mischievous, and serves as a constant companion to Seimei’s grandson, Masahiro.

Guren’s background is marked by a deep transgression and subsequent redemption. As Touda, he was a being of immense power, a lord of hellfire who was considered uncontrollable and destructive. His pivotal past act, which made him an outcast among his own kind and other shikigami, was an attempt to kill Seimei himself. Rather than destroying him, Seimei subjugated Guren and forged a regulating ring that allowed him to control his devastating powers, giving him the name Guren in the process. This act bound Guren to the Abe clan, and he was later charged with the secret duty of protecting the young Masahiro from the shadows, watching over him since childhood.

In terms of personality, Guren is complex and shifts with his forms. As Mokkun, he is often playful, sarcastic, and not afraid to voice his complaints, contrasting sharply with his intimidating true form. When he transforms into Guren, he becomes a serious, calm, and collected warrior, though a fierce and formidable presence remains just beneath the surface. His core motivation evolves from mere duty to genuine loyalty. Initially bound by his contract to Seimei, Guren ultimately dedicates himself to the service of Masahiro, believing in the boy’s potential to surpass his grandfather even when others do not. He chooses to become Masahiro’s guardian and partner, a bond that forms the emotional core of the story.

Guren’s role in the narrative is primarily that of a protector and mentor to Abe no Masahiro, the young onmyouji-in-training. He frequently steps in to rescue Masahiro from demons that the novice cannot yet handle, and their relationship gradually develops into a deep friendship built on trust and mutual respect. This relationship is key to Guren’s development. While other shikigami are initially resentful of Masahiro due to his inexperience, Guren remains a steadfast ally, and the boy’s unwavering faith in him helps Guren move past the guilt of his previous transgressions. His development reaches a critical point in the second major story arc, where he is taken and controlled by a powerful evil demon. This forces Masahiro into the heartbreaking position of possibly having to kill his closest friend and guardian to prevent the underworld from invading the human realm, a trial that tests the very foundations of their bond.

Among the other shikigami, Guren holds a unique position. While many resent him for his past attempt on their master’s life, he shares specific, close relationships with some, such as his bond with Kouchin, who is the only one to call him by a nickname, "Kou". His abilities are as formidable as his reputation suggests. As the most powerful of Seimei’s twelve shikigami, Guren is a master of fire, most notably being able to wield terrible and destructive hellfire. His true form is a humanoid demon of great size and strength, characterized by his long red hair and yellow eyes, and he is typically shirtless with a headband. The regulating ring created by Seimei is what allows him to channel this immense inferno without losing himself to the uncontrollable nature of Touda, making him a perfectly balanced and devastating force against the supernatural threats facing Kyoto.