In many Fairy Tail fanfictions, the battle between Natsu and Acnologia is often depicted as extremely epic. Natsu's fiery determination and his unique dragon - slayer magic make for an interesting contrast against Acnologia's overwhelming power. Some fanfictions might have Natsu discover new forms or powers in order to stand a chance against the fearsome Acnologia.
A common theme in such fanfictions is Natsu's unwavering courage when facing Acnologia. He might not be as strong as Acnologia at first, but his will to protect his friends and the Fairy Tail guild drives him forward. His dragon - slayer magic could potentially have some hidden aspects that are only revealed during this encounter.
If Natsu were trained by Acnologia, he might face a moral dilemma. Acnologia is a feared and often seen as an evil force. Natsu has always been on the side of good. So, during the training, he would have to decide whether to follow some of Acnologia's more ruthless ways of using power or stay true to his own values. This internal struggle could add a lot of depth to his character. Also, his relationships with his friends in Fairy Tail might be strained as they might be worried about the influence Acnologia has on him.
In the Fairy Tail universe, Igneel is extremely powerful with his fire - based magic. However, Acnologia is known as the most powerful dragon. I think Acnologia would win. His power is on a different level and he has shown to be nearly invincible in most battles.
The guild might see it as a call to action. They would come together to support Natsu in getting his power back. This could strengthen their bonds even more. Also, they might start to train harder to make up for the loss of Natsu's power.
One epic moment could be when Igneel unleashes his most powerful fire attack, a huge blaze that engulfs the area, and Acnologia just withstands it with his dark aura. Another could be when Acnologia lunges at Igneel with his massive jaws, and Igneel dodges at the last second.
One possible plot could be that there is some sort of misunderstanding or dark magic at play that causes Natsu and Mavis to fight. Natsu, being hot - headed, jumps into the fray without fully understanding the situation. Mavis, on the other hand, is trying to figure out a way to stop the fight without harming Natsu. As the battle progresses, they both start to realize that they are being manipulated and then team up to face the real enemy.
Some writers characterize Acnologia as a misunderstood loner. They show that his actions of destruction are a result of his past traumas. Others might make him more of a power - hungry villain who just wants to rule over all. There are also those who give him a sense of humor, which is a very different take from his usual brooding and menacing self in the original series.
In a fight between Natsu and Mavis in a fanfiction, it's really hard to say who would win. Natsu is extremely powerful with his dragon slayer magic, being able to take on some really tough foes. However, Mavis is the first master of Fairy Tail and has a great deal of wisdom and powerful magic herself. It could really go either way depending on how the fanfiction writer wants to portray the battle.
Perhaps the Fairy Tail members watching will have different reactions. Some might be worried for Natsu, especially those who are close to him like Lucy or Happy. Others, like Erza, might be more focused on analyzing Natsu's moves and Zero's counter - attacks. And there could be some comic relief from the likes of Gray, making snarky comments while still being engaged in the fight between Natsu and Zero.