Abe Seimei is the central figure of the anime, a master practitioner of onmyōdō living during the Heian period in the capital of Heian-kyō. He is a highly reclusive and misanthropic individual, preferring the solitude of his own complex on the outskirts of the city to the company of others at the imperial court. This isolation stems from a deeply painful past; orphaned at a young age, he was taken in by the onmyōji Tadayuki Kamo. Despite Kamo’s protection, Seimei was relentlessly bullied by other students due to rumors that he was the child of a fox spirit. His trust in others was shattered when a close friend named Masanaga, after being refused help to kill his own father, retaliated by sending thugs to murder Seimei. This betrayal convinced him that forming bonds with people only leads to tragedy, and he generally views human connections as a curse to be avoided.

In the story, Seimei serves as a supernatural investigator, using his formidable magical abilities to solve mysteries and deal with demons, ghosts, and other spiritual threats. His reputation is mixed; he is widely known for being rude, sarcastic, and insubordinate, yet his skill is so unparalleled that the court tolerates and fears him in equal measure. The central relationship of the narrative is his unlikely friendship with Minamoto no Hiromasa, an earnest and naive nobleman and a talented flutist. Hiromasa repeatedly seeks Seimei’s help with demonic incidents, initially against Seimei’s wishes. Over time, Hiromasa’s persistence and genuine, non-judgmental nature slowly break down Seimei’s emotional walls, and they become partners. Seimei also develops key relationships with others, including Lady Tsuyuko, a kind-hearted entomologist who becomes a loyal ally, and Ashiya Doman, a powerful and wicked female onmyōji who serves as his primary rival and often instigates supernatural problems for her own amusement.

Throughout the series, Seimei demonstrates significant character development. He begins as a detached, lonely figure who actively pushes others away, but gradually opens his heart to friendship and connection. This evolution is profound, reaching a point where he is willing to sacrifice his own soul to resurrect Hiromasa from death, proving how much he has come to value their bond. His past trauma regarding friendship and betrayal is confronted and healed through his new, positive relationships.

Seimei’s abilities are vast and rooted in the practice of onmyōdō. He possesses immense innate spiritual power, allowing him to see and sense supernatural phenomena clearly. His skills include creating powerful protective barriers using paper talismans, performing exorcisms to cleanse or destroy evil spirits, and binding spirits to paper dolls to act as his shikigami servants. He is also a renowned astrologer and master diviner. In his youth, he demonstrated a unique anti-yōkai ability that could drain a spirit’s energy, rendering it weak. He is often seen using a folding fan marked with a pentagram, which he employs as a tool for his spells, and is known for being highly intelligent and a master of strategy in his confrontations with the supernatural.