One of the most exciting moments is when Natsu's intense fire magic clashes with Jellal's powerful Heavenly Body Magic. The visual display of their powers colliding is just amazing. Another great moment could be when they exchange some intense verbal sparring before the actual fight, adding more tension to the encounter.
Well, this fanfiction could depict Natsu's power evolving during the fight. Maybe he discovers new ways to use his fire magic because of the intense battle with Jellal. Jellal's power might be shown as having hidden depths. His spells could have secondary effects that are only revealed as the fight progresses, which is different from how his powers are usually shown in the main series.
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.
Natsu would probably be really excited. He'd be looking forward to having a new little friend to play with and might even start thinking up crazy names for the baby. Lucy would be very supportive, offering Erza advice on pregnancy and motherhood, perhaps sharing some of her own experiences or knowledge from books she's read.
Gray would be shocked at first. He and Natsu have a long - standing rivalry - but also a deep friendship. He might initially be angry that Natsu would just leave like that, but then he would realize how much he'll miss him. He might also feel a sense of loss for the guild as a whole, since Natsu is such an important part of it.
Natsu would likely be extremely hurt. He has always been loyal to Fairy Tail, so being betrayed would be a huge blow. He might initially be in disbelief, not wanting to accept that his friends and guildmates could turn on him.
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.
One great fanfic about Erza and Jellal could be 'The Redemption of Jellal in Erza's Eyes'. In this fanfic, it focuses on how Erza's presence and her unwavering belief in Jellal's ability to change start to influence him. It shows their interactions in a post - Tower of Heaven scenario, where Jellal is trying to come to terms with his past actions while Erza is there to support him, but also not let him off the hook easily.
The guild would likely be shocked at first. They consider Natsu as one of their own, so his attack would be completely unexpected. Some members might try to talk him down, like Lucy. She has a close bond with Natsu and would probably try to reason with him.