This is the story of Ciel and Sebastian traveling around the world after becoming a demon.
There are medieval Europe and the world, modern times, other worlds, and a wide variety of topics. (That's why it's a long story. Mina who don't like to wait can read it before reading it or poke the upper right corner.) The devil has no blood, no heart, no fixed form, no need to eat, no fear of sunlight, and follows desires. So during the journey, the devil exchanged his souls with the devil and reached a soul contract.
Soul Contract: Both parties are unaware of it. When the conditions are met, the Supreme Law will decide whether it is achieved. Both parties cannot abandon it. The name of the soul of the other party is imprinted on their own souls and cannot be annihilated. Even if the soul is dispersed, it will exist in eternity. After reaching the goal, the opponent's words (yes, this meme ╮(╯▽╰)╭) will appear on the chest and become "heart".
Protagonist: Ciel (13 years old, theoretically unable to grow up, devil), Sebastian (age unknown, devil butler)