I'm the Blade Saint. It's Only Natural to Slaughter My Way Through the Demon Caves

Power fantasy + one female lead + no System + invincible protagonist + dual blades

In 1773, an unknown purple gas appeared across the world. Anyone who entered it became a mindless demon.

In 1800, humans discovered that some hideous demonic beasts had begun appearing inside the purple gas.

In 1805, scientists named the purple gas "Purple Mist."

In 1850, demonic beasts launched massive attacks on nearby nations and cities, putting human civilization on the brink of destruction.

In 1855, scientists discovered that humans could cultivate using the vital energy within their bodies. Thus began the era of martial arts for all.