The Final Sin: Nanatsu No Taizai

Acnologia after his supposed defeat at the hands of Natsu, finds himself in a strange land in the middle of a war.
Having lost his time rift abilities, and been drained of most of his magic, he needs to lay low and wait while his magic regenerates, as he does so he meets an odd group of friends, who give him shelter, food and even healing for his injuries, he learns that they call themselves The Seven Deadly Sins and they fight, to protect the world and atone for their sins.
As time passes he slowly begins to realize what the Flame Dragon King, Natsu had told him was true... and that his sin, was the sin of hatred.
As the war rages on, a warrior appears on the battle field. The 7th Deadly Sin, The Demons Sin of Hatred Acnologia who will serve as a replacement for one of the fallen sins.