Robin must have been at least 10,000 ft above ground from where he was, he could see the clouds zoom by him as the Grima drew closer towards Ylisstol. Even from this high up, the Ylissean capital's high walls and decorated spires were visible from where he stood.
Grima's objective was simple. Make a statement -burn down the entire world, starting with Ylisstol- and make the Shepherds watch helplessly while doing it, and then kill them. Robin knew that Grima was more than just cruel, spiteful, and malevolent. He was petty. He wanted to humiliate and toy his prey before killing them, taking in the pain and suffering of their victim's anguish before finishing them off in the bloodiest of fashion. Grima didn't just want to kill Robin, Chrom, and the Shepherds. The Fel-Dragon wanted to kill them after destroying everything they love while they were too powerless to stop him.
That's where Grima's wrong though. Through his arrogance, he left an opening for Robin and the Shepherds to take advantage of. With the Awakening ritual complete and with the teleportation rites from Origin Peak complete, the Shepherds had a fighting chance. Instead of being caught helplessly on the ground, watching the world burn at the Fel-Dragon's pleasure. It looked like no more than a 60 km dash from where he was Robin estimated. He supposed that was the best Naga could get to them but given Grima's size, better than from the tail end.
As Naga mentioned earlier before they completed their teleportation, either Chrom or Robin had to finish the final blow for this to end. If the former deals the killing blow, Grima is sealed for another millennium. If Robin made the final blow, Grima would be gone forever. Despite the opposition from Chrom and the rest of the Shepherds, Robin wanted to make it so that he committed the final blow.
Robin and the Shepherds were on borrowed time. The only thing keeping himself, Chrom, and the Shepherds from flying straight off of Grima's body is a combination of willpower and magical exertion from Naga herself. They were standing in a wedge near the nape of the foul beast's neck. From afar stood a single man in a black overcoat, his body radiated around him almost as hungry tendrils waiting to strike the nearest threat to its host. It was the hierophant, Grima's vessel, the mortal conduit that kept Grima's draconic form sustainable in reality, the true leader of the Grimleal, it was Robin himself in another time if Grima had his way. Warping around the hierophant were scores of elite Grimleal chosen, some were mounted while others fought on foot, all radiating the same malevolent purple energy from their eyes as their dark master.
It was going to be a hard slog between Grima's servants the hierophant himself, Naga knows how many reserves the Fel-Dragon has at his disposal to throw at him, and that is of course not getting to the danger that the hierophant poses himself.
Chrom reassured Robin with a hand on his shoulder,
"I'm with you the whole way."
"You too, buddy. You too."
The Shepherds charged wordlessly across the dragon's neck at the command of Robin's hand signal with weapons drawn and hearts brimming with purpose. A handful of Chosen would sprinkle out from the warp points and trickle towards the Shepherds were cut down at no loss of speed. Against more comprehensive groups of Chosen formed up into improvised shield walls standing between them and the Hierophant, Robin signaled for the Shepherd mages to launch a coordinated volley of magic to Shepherds were a well-oiled machine, warriors that would have been more than a match for any nation's elite troops are falling in large numbers and the Hierophant is staring at Shepherd's progress in a mix of amusement and annoyance.
On their way to the Hierophant, Robin noticed a series of warp points where Grimleal chosen were streaming in. He figured if a portion of Shepherds can keep them occupied, that would give the rest enough time to finish off Grima. Robin ordered the Shepherds to force the Grimleal to "run the gauntlet through those warp points". With those words in mind, the magic-using members of the Shepherds started pre-emptively hurling spells against the warp points, creating an area that passively damaged any chosen that spawned. Vulnerable and weakened, the handful of Chosen would be suppressed by constant volley fire from Shepherd archers like Virion and Noire. Pelted with arrows, buffeted by flame, and blocked by walls of ice, the Chosen would have to contend with a final barrier of shields, armor, and weapons from Shepherd's melee contingent who serve s a blocking force at the end of each gauntlet to stop any remaining stragglers.
The vast tide of chosen gradually trickled into a stream, giving Robin and his chosen detachment of combat pairs the chance to finish off the Hierophant once and for all. The four-remaining pair of Shepherds: Robin & Chrom, Cordelia & Sumia, Cynthia & Lucina, and Morgan & Severa ran the last dozen kilometers between where they last stood and where the Hierophant stood, defiant and imperious of their advance.
First came a volley of spells from Robin, Morgan, and Cordelia. Gouts of flame, massive cutting waves of wind, and columns of crackling thunder crashed into Grima's mortal vessel. Some of the magical spells were countered by the foul energies surrounding the Fel-Dragon but some spells went through the Fel-Dragon seemed more annoyed than anything else. The Hierophant's body remained largely undamaged.
Grima, still standing confidently and coursing with energy, took on all the Shepherds even as they attacked in unison or as pairs. Attacks from both sides were dodged, parried, or blocked through magical wards either from Robin or Grima. Both sides displayed agility and situational awareness that could only be honed through years of experience, magical enhancements, and divine provenance from above. Grima's energy field remained strong all around, Robin noticed that the field of energy around the Hierophant is a sliver thinner now than it was at the beginning of the fight. From there, the Grandmaster began devising a new plan.
But before that, the Shepherds had to endure Grima's inevitable reprisal.
In the midst of the furious melee, the Hierophant temporarily suspended his body mid-air and pointed his finger at the formation of shepherds maintaining the gauntlets against the waves of Grimleal Chosen. On command, the massive form of the Fel-Dragon's head turned at the command of its vessel and leveled its head to unleash a torrent of dark flame.
Robin quickly signaled Cordelia to transport him to higher ground to deliver a message to the other Shepherds. Robin boarded her Pegasus and together they flew back above the general area where the formation leaders managing the gauntlets: Frederick, Viron, and Miriel noticed temporarily while moving up while telling their subordinates to continue business as always. Robin issued hand signals to order them to fan out and disperse the gauntlet, get ready for general close combat, large area attack incoming. He cast a project image spell on his hand signals to ensure that the formation leaders and members of the gauntlet got a clear view of what they needed to see and what was about to happen next.
As soon as the Fel-Dragon released a stream of its noxious flame breath upon the nape of its neck, the gauntlets were already dispersed and safely out of the way. The only targets left were the dozens of Chosen that spawned without the hindrance of the gauntlet keeping them suppressed, blocked, or killed. In moments, the bodies of the chosen melted into an incomprehensible pile of slag and slime. Frederick and many of the other Shepherds maintaining the gauntlet barely concealed their disgust and horror as they saw many Grimleal Chosen die with rabid smiles on their faces as they embraced Grima's "blessing". All that was left was a pile of goop where the Chosen victims stood.
More Chosen would spawn from where their comrades had been slain which kept the gauntlet Shepherds occupied. Robin's stunt seemed to have broken a nerve in the Hierophant's ego who now turned towards him and Cordelia in the air.
Frustrated, the Hierophant waved his hand in frustration and the head of the Fel-Dragon returned to its original pose. The vessel drew forth a Levin Sword crackling with violet energy and pointed his blade at Robin and Cordelia. The Hierophant let out ragged laughter that boomed around them.
"RETURN TO ME…COME…WE ARE ONE…AND THE SAME…", the Hierophant boomed at Robin while bolts of purple lightning crackled from his blade.
Robin could not respond at first. But soon after Grima fired the first bolt of lightning at him, he could feel an aching pain coursing through his body. In a flash, he heard the sound of a woman and a man frantically saying "No!" simultaneously before screaming in excruciating pain. The vision left Robin open for the bolt of lightning and it would have nearly killed him had Cordelia not successfully jinked with her Pegasus in time.
The sudden movement of Cordelia's Pegasus knocked Robin out of his trance and back into reality. His beloved Cordelia gave him a reassuring smile.
"We're all right here by your side!"
Robin smiled at his lover's encouragement, "Then let us finish this fight, together!"
He had no time to dwell on such issues; he had a dragon to slay this day.
This was it, do or die. Cordelia dove towards the Hierophant, taking evasive maneuvers to any errant bolts while returning with wind magic in kind. The magic had little effect on the target but it was enough of a distraction for Robin to make a carefully timed jump off of her Pegasus. With Mercurius grasped in both hands, Robin lunged at the Hierophant from the air. The same magical sigil that Robin has seen before flashed from his blade. The symbol only activates when Robin, Severa, or Morgan need to hit an enemy with a powerful.
Robin's initial blow crashed against the Hierophant's form. His aura of dark energy briefly collapsed before the Fel-Dragon regained his composure and began to fight Robin in a furious duel.
Both combatants flung powerful spells at each other and each successive attack was either dodged or absorbed. The initial exchange of magic between Robin and Hierophant is then followed up by a flurry of melee attacks at all sides from the other Shepherds. The Hierophant's parries and dodges were only marginally worse this time around but for each successive round of combat, the Hierophant's energy field became dimmer and dimmer. His ability to dodge and parry attacks became sloppier and more attacks landed to further drain his protective energy. Robin and the Shepherds for their part displayed an impeccable talent of dodging, weaving, and pushing each other out of the way of otherwise lethal blows.
Soon the Hierophant's energy field shattered and dispersed from his body after Robin scored a critical hit with a well-aimed Thoron bolt. The Hierophant was then assailed by the Shepherds with bloody results. A sword cut from Severa to the left arm, a Rexflame bolt torching his right arm and disabling his arm from Morgan. Multiple lance wounds to the front and back from a dozen or so triangle attacks from Sumia, Cordelia, and Cynthia. Sword cuts to his legs and his upper torso courtesy of Lucina and Chrom.
Robin, seeing his chance let loose a final column of thoron against the Hierophant before closing in with Mercurius. Unlike his previous attacks, Robin could feel the agonizing pain of the lightning swell across his body as these attacks were against the Hierophant's form itself and not the energy field. Robin gritted his teeth and kept charging forward, sword tightly gripped in two hands. The other Shepherds were initially distracted with dodging incoming attacks to notice Robin's advance.
It was only until Cordelia, after dodging a series of lightning bolts from the Hierophant's Levin Sword finally realized Robin's intentions. She was horrified,
"Robin, no! What are you doing!?"
Upon hearing those words, Chrom and Lucina sprang into action after a brief pause hoping seal Grima before Robin does the unthinkable. It was a race to see who gets to inflict the final blow against the Fel-Dragon. The Hierophant concentrated all attacks on Robin but his weakened state meant any attacks were either dodged or countered. The surrounding Shepherds stopped to witness the horror of the race happening in front of them.
The last moments of the fight were tense as Grima's host made his last stand parrying incoming attacks from Robin, Chrom, and Lucina. Each is desperate to land the final blow themselves in order to achieve their desired end goal but without pushing against each other. Despite the chaos of the melee at hand, it was Robin that made the final blow against the fell dragon.
Grima roared in agony as Robin drove Mercurius through his host's abdomen, the sacred blade had pierced the Hierophant to the hilt. A stream of blood spewed from the blade's entrance and both combatants collapsed to the ground. Because the blow was inflicted against another version of himself, Robin could feel every bit of pain from the sword blow as Grima. He hoped it was enough to win the day.
Luckily, Robin was right as he noticed the body of himself and the Hierophant started decaying and flickering away from existence. Starting with his right hand, he could see parts of it slowly decay and disappear. Robin smiled in relief, knowing that what was necessary was done. He won't live to see the future he has secured for Cordelia, Morgan, or Severa but he hoped they would understand why he went with this decision on this fateful day.
The Hierophant for his part laid still, body splayed in all directions in a pool of his own blood, and started …crying? What started off as a well of tears eventually became a mumbling series of questions of "where am I?" and "who are you, people?"
When Chrom approached Robin and the Hierophant, the vessel let out a weak cry and asked "Di-, Dimitri? Your highness? Is that you?" Chrom and Lucina ignored Hierophant's confused ramblings and went to see Robin. Upon seeing Lucina, the Hierophant started mumbling something about "I—In, Ing,,,grid. I-I love you…I don't want to leave you! Not like this!"
The other Shepherds trickled in and awkwardly shuffled past the Hierophant as he continued mumbling more regrets,
"F-Felix…I'm sorry, I have failed you…I was a bad…b-brother." Out of all the ramblings from the Hierophant, this one that hit Robin the most. He wasn't sure why but he was too weak at process the idea any deeper than the surface.
Chrom crouched next to Robin's body and shook his head,
"My friend…you actually did it didn't you?"
Robin nodded weakly and smiled.
He was light at the head at this point, his hands had fully disappeared and now his arms are decaying into nothingness as well. He glances over at the Hierophant and noticed that his body was decaying at a similar rate. But his brief moment of triumph was broken when Cordelia alongside his daughters. Their collective expression was that of sorrow, anger, and sadness.
Robin would have remarked on how beautiful she looked if he had the strength to speak. He could feel the strong, comforting grip of her hand under his head lift him up. She started saying something to Robin. He could only hear the faint pitch of Cordelia's voice but could not understand what she was saying, Robin thought she was either angry or concerned. Behind Cordelia, Robin could faintly see Lucina and Cynthia comforting a crying Severa and Morgan as they were both probably wishing their father wouldn't disappear from existence a second time.
The next few minutes was that of silence as the remainder of Robin's body disappeared. Cordelia at this point stopped crying and stared into the face of her husband one last time before he faded from existence. Robin for his part, gave a weak smile to the weeping Pegasus Knight.
Robin's world went white as what remained of his form disappeared into nothingness.