For over centuries, an organization called the Demon Slayer Corps has protected humanity from flesh eating creatures called demons. No one knows exactly when they first appeared. However, demons have always hunted and killed humans. But when word gets out about a stranger killing demons outside of the Demon Slayer Corps, the Water Pillar, Giyuu Tomioka, is sent on a mission to search for the one they call, Mayonaka Kyūseishu. On a dark and sinister night, Giyuu finds himself face to face with a blood-thirsty demon. However, just before the demon could end Giyuu's life for good, he was saved and rescued by a stranger with breathtaking crystal blue eyes. Who is this stranger? And how will they suddenly change the stoic, cold-hearted Pillar's life forever?