Dōma Hoshi is an ancient priest and a central antagonist in Garo: Crimson Moon, acting as a primary source of evil and manipulation behind the horrors that plague the capital. His background is defined by his role as a mentor to significant onmyōji, having been the teacher of the renowned Abe no Seimei. His past, however, is deeply corrupted; he is known to have taken sexual advantage of his pupil, Seimei, and placed a powerful curse upon her that would have lasting consequences for her future. He also served as the manipulative mentor of his successor, Ashiya Douman.

Personality-wise, Dōma Hoshi is the embodiment of a sinister and calculating mastermind. He is devoid of empathy and driven by a desire for ultimate destruction, orchestrating numerous Horror attacks on the capital from the shadows. His motivations are grand in scale and purely malevolent, aiming to unleash an ancient Horror of immense power, Rudra the Catastrophe, to cover the world in darkness. To achieve this, he engineered a complex plan to trap his former pupil, Abe no Seimei, turning her into a vessel for the Horror Rudra so it could consume the entire world.

Within the story, Dōma Hoshi holds the pivotal role of the evil mastermind whose machinations drive the central conflict. He is the source of the curse affecting Seimei, which feeds on the darkness inside her and weakens her powers as she gives in to her desire to destroy her enemies. Working in tandem with Ashiya Douman, he calls upon Horrors to attack strongholds like the Light Palace and manipulates events to strengthen the Crimson Moon, which serves as a seal for Rudra. His ultimate goal is to break this seal, merge the realms of the living and the demonic, and plunge the world into chaos.

Key relationships define his villainy. His relationship with Abe no Seimei is one of profound betrayal, as he moved from being her teacher to her abuser and tormentor, placing a curse on her to serve his apocalyptic scheme. He also shares a manipulative bond with Ashiya Douman, acting as an evil mentor who guides Douman to further his dark ambitions, eventually leading to Douman merging with the freed Horror Rudra. The narrative shows him as a consummate schemer; however, information on any personal development or redemption arc is absent, as he remains a static and purely antagonistic force whose defeat stops the resurrection of the ancient Horror lord. His notable abilities are connected to his ancient priestly powers, which allow him to mastermind complex supernatural rituals, place lasting curses on powerful onmyōji, and call upon and control Horrors to attack the capital.