GARO.

Garo focuses on Kouga Saezima, the current possessor of the title, Golden Knight Garo, who protects humanity against dark demonic infestations called Horrors. One day he meets a young girl named Kaoru whom he saves from a horror, but gets stained with horror's blood. The makai knights have the rule that those that have been stained by the blood of a horror shall be executed before experiencing a painful death after approximately 100 days.