The Demon Prince and the Warrior Princess (F...
Natsu Dragneel, nicknamed E.N.D. or the Demon Prince, is Prince of the Alvarez Empire and the younger brother of Zeref Dragneel. Erza Scarlet, nicknamed Titania or the Warrior Princess, is the princess of Fairy Tail Kingdom. Due to a chance encounter they fall in love. But a demon prince and a mortal princess' love is taboo, and tragedy is sure to strike. E.N.D!Natsu x Erza. AU.
(Note: it's Erza Scarlet on the cover, not Erza Knightwalker. This is an alternate universe where Erza's battle uniform is Knightwalker's attire)