The Secret Sin

This is a tale of ancient times. An era before the human and non-human worlds were forever divided. When the Holy Knights defended the realm, wielding their magical powers, they were feared and highly respected. But among them, a group emerged that betrayed the kingdom and became mortal enemies to all Holy Knights. They are known throughout the land, as the Seven Deadly Sins. But there was another framed for the murder of Grand Master Zaratrost, she's the illusive eighth sin.
Her name is Adeline, Ghost Sin of Despair. She fled with Merlin, taking refuge in the Kingdom of Camelot, under the protection of the King.
The King passes and Arthur Pendragon takes his rightful place as the next King of Camelot.
News of the troubles in Liones makes it way to Camelot, peeking Adeline and Merlin's interest. They travel to Liones with Arthur and end up helping their old Comrades.
Everyone thinks they've won, but the war has just begun. With the Ten Commandments free, Meliodas and Adeline must face the truth about their past and destroy their old enemies.
~
Obviously I don't own the plot for The Seven Deadly Sins/Nanatsu no Taizai, but I do own Adeline and everything she brings. If you haven't read the manga, this won't make much sense as the major part of this story hasn't been released for the anime, yet.