MTL - I, a Demon Slayer Girl, is Invincible! - Chapter 271

"Be my son's mother."

The story is about a boy entering high school, who answers a strange call from a public phone one night. The caller challenges him to a bet: She’ll remove the birthmark which he sees as the cause of so many problems, and he’ll have fifty days to win the heart of a girl he’d considered far beyond his reach. And with this, a very strange summer begins.

Once upon a time, there was an office worker who was dragged by his boss to take a hot spring bath. While he was soaking…

This is probably very serious. He came to a Beast world and was licked out of his sleep by a golden lion. The lion accompanied him. Only then did he understood this world… when he came to the lion’s tribe, he found that this was really not an experimental base…

- Description from Novelupdates

The formless ancient world was infested with despicable demons. They hunted and feasted on mankind, keeping the human civilization constantly in a weak and suppressed state.

During the first known year, a magical mountain descended into the world from the realm of the Gods. Carved on this enormous mountain was a message: ‘Heaven Prevails’…

After the Grand Descent, a name that was given to the descending of the mountain, the Three Great Sages made their ways to Mystic Mountain where they learned to harvest what we now call magic, establishing the Mystic Cults and eighty-one sacred shrines to help aid mankind with the cult’s mystic powers against the eternal fight to the death with demons.

- Description from Novelupdates