Garo focuses on the life of Kouga Saejima, who has assumed the title of Makai Knight to protect humanity against dark demonic manifestations called "Horrors". In his quest to purge them, he encounters a young girl named Kaoru whom he saves from a Horror, but learns that she is stained with its demonic blood. As a rule, those that have been stained by the blood of a Horror shall be cut down, or else they will die painfully in approximately 100 days. Kouga spares Kaoru and tries to find a way to purify her before her remaining time expires. Thus, the series focuses on Kouga's developing relationship with Kaoru and his stand in protecting humanity in accordance with the wishes of his father, the previous Garo. In the process, encountering another Makai Knight named Rei Suzumura who eventually becomes his ally, Kouga confronts his father's former disciple who is also the cause of a recent string of Horror attacks in preparation of a more sinister advent of the Horrors' originator, Messiah.