Ghoul ga Sekai wo Sukutta Koto wo Watashi dake ga shitteiru is a Manga/Manhwa/Manhua in english language, ACTION series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

“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.