"Fairy Tail" chapter 505 saw the sudden death of Makarov when he used the Fairy Law ability to defeat the invading warriors of Alvarez. In chapter 506 the news of his death will be reaching Gray and Natsu Dragneel, and this may knock the two former friends back to their senses and stop fighting each other to avenge Makarov's death.
As reported by iTech Post, Lucy, Wendy, and Ezra may be able to stop the two from killing each other just in time for them to discover Makarov's recent death. This may force Natsu and Gray to put their issues aside and rush in to help Mavis and the rest of the Fairy Tail guild defeat the remaining Alvarez soldiers.
Mavis, on the other hand, won't be able to wait for Natsu and his companions to arrive, and she will storm the guild to battle.
However, it is also hinted that this truce will not last that long given that Natsu has been revealed to be E.N.D., the entity created by Zeref himself. Fans of the series will recall that Zeref created Natsu as a reincarnated form of his dead brother and that Natsu, as E.N.D., has a mission of ending Zeref's curse of immortality.
This does not sit well with Gray, given that his backstory reveals he was affected by the attack of Etherious Deliora when he was just a boy and because he inherited the role of demon slayer.
Game N Guide reveals, however, that even Gray may not be able to defeat Natsu in the end as Natsu was made with the sole purpose of destroying Zeref. This would indicate that Natsu is far more powerful, and their raid to help the Fairy Tail Guild from the enemy will showcase the gap between Natsu and Gray's abilities.
"Fairy Tail" chapter 506 is scheduled to roll out next week.
