Legend of the Fire Demon

Natsu Dragneel is a dangerous demon that was sealed away in the Book of END. Then one day, a young wizard named Lucy Hearfilia accidentally sets him free. According to Natsu, Lucy was his former lover that he had brought back to life. He's not willing to lose her again, even if it means going against his brother Zeref the god of death who wants to drag Lucy back to the Underworld.