Only I Know the Ghoul Saved the World Manga

A brief description of the manga Only I Know the Ghoul Saved the World:

“I’m not a hero. I’m a monster that devours monsters.” In a chaotic world where ferocious monsters run rampant, there was a “monster” who inherited the title of “hero” in the holy city, the last bastion of humanity on the brink of extinction. Alice, a rookie adventurer, was attacked by a large pack of dog people (Kobolds) during her first ‘dungeon’ exploration. The one who saved her life was Leon, the third-generation “Savior” hero, who, despite having the body of a monster (Ghoul), possesses a human heart.

“I’m nothing but a defiled ghoul who keeps on killing monsters.”

“No, you’re the only hero who can save the world.”

For some reason, Alice, who admires him, applies to become Leon’s disciple.