Natsu Dragneel vs. Zeref Dragneel

Natsu Dragneel vs. Zeref Dragneel is a fight fought between the Mage of Fairy Tail, the Fire Dragon Slayer Natsu Dragneel and the Black Mage, also known as the Emperor Spriggan, Zeref Dragneel.

Prologue
Having defended against the first wave of the Alvarez Empire's assault, the Fairy Tail members gather at the guild hall to discuss the situation, facing enemies from every direction. Even though Mavis originally disagrees with getting others involved, she eventually accepts the idea of Mages outside of Fairy Tail helping. While Lucy tries to question the now-captured Brandish, the western army of the Alvarez Empire lead by Zeref receives the news of Brandish and Ajeel's defeats. Upon hearing this, Zeref smiles, noting that otherwise, the things would be boring, however, he also points out that Fairy Tail not killing their enemies is their weakness. Meanwhile, the news from the east arrive and Fairy Tail Mages learn that all of Bosco's guilds have been defeated. However, the Mages of Fiore also move out, with Sabertooth and Blue Pegasus going to intercept the army coming from the north, Mermaid Heel and Lamia Scale heading out to liberate Hargeon Town in the south. Several Fairy Tail Mages are sent to help those out, however, they soon notice that Natsu, who is supposed to join one of those groups, is nowhere to be found. After it is revealed that Four Gods of Ishgar will face the greatest threat coming from the east, Natsu's location finally becomes known and everyone witnesses the Fire Dragon Slayer flying towards their main enemy, Zeref.

This causes a discord between Erza and Gray, with the two disagreeing on whether to trust Natsu and his reckless action. However, eventually, the Mages agree to follow the original plan and leave Zeref to Natsu. Meanwhile, Natsu makes the first contact with the enemy forces, charging straight into them with an intention to make Zeref appear. He takes out a huge number of soldiers, using his Magic for both offense and defense as the Alvarez soldiers fire back with their ranged weapons. Even though it seems like Natsu gets overwhelmed by these attacks, he quickly replies with Fire Dragon King's Roar, eliminating almost thousand soldiers in total by that point. Finally, Zeref makes an appearance and Natsu notes that he thought it'd take more than that to make the big guy come out. As Zeref replies that he wanted to see Natsu as soon as possible, the Fire Dragon Slayer gets ready, removing the bandage from his right arm. Before they start, however, Zeref orders Invel to move the army away and Natsu tells Happy to fly away as well.

Battle
As Natsu states that they will not hand over Mavis and Zeref blames the current circumstances on Natsu, claiming that he was unable to destroy him, the Fire Dragon Slayer reveals the tattoo of a Dragon on his right arm that was hidden by the bandages and Zeref notices an immense amount of Magic, as well as intense heat coming from Natsu. The Dragon Slayer smirks as he charges at Zeref, delivering a crushing punch followed up by his flames and Zeref crashes through the hill in the area thanks to the force of the attack. However, he jumps out and shoots his Black Magic towards Natsu, which the Fire Dragon Slayer burns out, much to Zeref's shock. Making the use of his speed, Natsu instantly appears in front of Zeref and before he can react, the Black Magic takes yet another attack from Natsu, an attack that keeps growing in power as an entire landscape falls to Natsu's flames.

The Dragon Slayer continues with a barrage of attacks and Zeref is the target of several explosive strikes. However, in spite of this, Zeref smiles and launches an attack of his own which injures Natsu to the point of burning off some skin on Natsu's face and the two keep on clashing afterwards. Zeref then backs away for the moment to comment on Natsu's newfound power, wondering where it comes from. Natsu explains that he has inherited it from Igneel as the last power that the Fire Dragon has left inside him, having taking 10 months of training in order to unleash it. Zeref is surprised and Natsu further explains that it is a one-time deal that, after it is used up, will never regenerate. Zeref finds hope in these words, realizing that as it is a power granted from the dead, it may be able to destroy an immortal. Natsu then taps into this power and activates Fire Dragon King Mode and a surprised Zeref commends this, watching as even the ground begins burning. Natsu yells out that he is ending this right now and Zeref, relieved that his wish is about to come true, gives his thanks to Igneel, Anna, Layla and Natsu, as his little brother hits him with the attack, seemingly destroying the Black Mage completely.

While Invel watches all of this, surprised, Happy's smile soon changes to a worried expression as Natsu falls on his knees, seemingly exhausted. The Dragon Slayer then claims that he's okay, saying that he has enough of power for one more strike, just as the dust clears out, revealing a figure of now-injured Zeref. While Natsu begs Igneel to lend him his power for one more blow, Zeref puts on his usual smile and states that the Dragon Slayer has attained great strength. The Black Mage reveals that he has always hoped that Natsu would be able to stop him, however, he also says that he thought it was too late as Zeref had decided to destroy the world instead. Seeing Natsu's current strength, however, Zeref once again begins to hope that his younger brother would be able to end him and so, he decides to reveal something important: his name being Zeref Dragneel and his identity being an older brother of Natsu. The Black Mage further explains that 400 years ago, his parents, along with his little brother Natsu, were killed by Dragons and so Zeref began his research of creating Demons, with Natsu being E.N.D., "Etherious Natsu Dragneel".

Natsu refuses to accept this, claiming that he's not the one who created Tartaros and Zeref corrects him, stating that it was just Mard Geer using the Book of E.N.D. to band the Demons together with a common goal. Summoning the very book, Zeref shoots through it, causing Natsu an immense pain as the Black Mage explains that he eventually let Igneel take care of the now-revived Natsu and he, along with 4 other children and their Dragons travelled through Eclipse to present from 400 years ago thanks to Anna and Layla's assistance. Zeref continues, claiming that waiting for 400 years was hard as a lot happened, until he mentions Mavis, which is when Natsu loses his patience and charges at Zeref. In the middle of this, Zeref reveals one more thing: as a Demon from the Books of Zeref, Natsu will cease to exist if his creator dies. Paying no attention to this, Natsu states his resolve, wanting to erase Zeref. However, it is Happy that stops Natsu and even though the latter protests, the former says that he doesn't want Natsu to die. As Igneel's power is fading, Happy yells out that Natsu is his best friend and he is taking him home. Natsu accepts it and the two fly away, while Zeref with a smile on his face, thinks to himself that Natsu is no longer able to stop him and bids farewell to his younger brother.

Aftermath
Afterwards, Invel approaches Zeref, witnessing the Emperor's injuries disappearing instantly. Zeref states that as there is no one capable of stopping him anymore, any hesitation wihin him is gone. He tells Invel to continue the army's advance, intending to conquer Fairy Tail and capture Fairy Heart. As Invel accepts these orders, Zeref presents one more request - new clothes for him, something more befitting an Emperor. Meanwhile, Natsu and Happy stop by a lake inside a forest to rest. Natsu wonders if Happy's paws are alright and as the Exceed washes them in the water, he states that they are just fine. Recalling what just happened and what they learnt about Natsu's identity, Happy speaks up, claiming that the two of them will always be best friends no matter what. As Natsu confirms it, Happy runs towards him, hugging him and, with tears in his eyes, hoping to find another way so that Natsu doesn't have to die.

Meanwhile, the battles against the Alvarez Empire proceed into the next stage. Lamia Scale and Mermaid Heel commence the mission to liberate Hargeon Town and stand against Dimaria and Wahl, and their armies. Elsewhere, Sabertooth and Blue Pegasus are already fighting off the soldiers, meeting up with the fearsome Bradman and in the east, Four Gods of Ishgar face God Serena, August and Jacob.