The Son of a Dragon God (Adoption)
Natsu is left alone by his guild as they were put to sleep by Makarov and Gray. As Natsu struggled in the battle against Acnologia. Acnologia saw that Natsu was determined to not give in a battle he knew was futile. So Acnologia gave Natsu a deal. Become his Foster son and become a DemiGod of Dragons or Lose his life...