A ripple of force pulsed through the air, launching the bodies back. They rag-dolled as they hit the ground. A younger boy hit a table wrong, bending his neck in an unnatural way. Despite this, he lifted himself up, not even bothering to right his neck.
Harry girded himself, directing his attention towards Riddle, while Wanda, Ginny, and Lily guarded his flanks. "You take them, I'll take him." Harry said quickly.
"Oh, but all of this is me." Riddle said, flinging killing curses from his wand. Harry met them with his staff, deflecting them away, but their paths bent in the air, boomeranging back around. Harry materialized stone around the curses. He contained the detonations this caused, triggering a series of muffled whumps around him. He tapped into the power stone and channeled the energy from each of these explosions into beams that streaked back towards Riddle.
Riddle danced away from the first barrage, his body moving unnaturally, more like an animated character than a real human being. Harry arced the beams around to follow him. The student's bodies flung themselves in their path, but the stream of energy lanced through them uninterrupted, and not one of the human shields appeared phased by having holes carved into their bodies.
None of these drones were particularly adept in a fight, casting spells without much accuracy or speed. However, the sheer number of them, and their seeming indestructibility, still made them a problem. Lily was absorbing as many of the spells as she could, avoiding the many dark curses. Ginny and Wanda took care of those by intercepting them with benches, plates, cups, rubble- whatever was at hand.
Wanda had the solution. The harsh light of Harry's spells cast the room in a sharp contrast of light and shadow. Wanda stepped into one of the shadows- cast by an overturned table- and vanished. Then half the students- those standing in shadow- vanished too. As Harry's beams bent after Riddle, the shadows rotated, swallowing up more students.
Finally, one of Harry's attacks hit its mark, sparking like a firework when it struck a bubble shield Riddle had summoned at the last second. The shield shattered, casting fragments across the room that sparked and jittered across the floor. Harry lifted up these fragments and propelled them towards Riddle. He was forced to summon another shield, and the fragments broke into multicolored sparks as they impacted.
Riddle bounced back up, and Harry transfigured the air around him into steel, forming a solid block of metal that encased Riddle. Just as quickly, the metal vanished, but Harry followed that up by vanishing the air around Riddle and forming a bubble charm around him. His pale face went somehow paler as he tried to rasp for breath. He punctured the bubble, and the air rushed back in with a pop, but Harry wasn't done. He transformed Riddles' robes into hornets. Riddle cast off a burst of fire the purge the swarm, but at the cost of his dignity. Harry was unnerved to find that he was built like a Ken doll. "What did you do to yourself?" He asked.
Riddle's grin was manic. "So much. I have you to thank for this, actually."
"Me?"
"Believe it or not, Harry, but I am capable of learning from my mistakes." He shook his head. "I saw what became of me, if I were to go down the path of splitting my soul into Horcruxes… I would be reducing myself. Splintering my soul into smaller and smaller fragments."
He stepped forward, robes materializing around him. "So I thought… what if I did the opposite. What if I grew my soul?"
Harry blinked, casting a glance towards Ginny who looked even more unnerved and bewildered. "And you did that… by killing hundreds of children."
"I needed fuel." He waved his hand casually. "But of course, this body was no longer sufficient to contain me. I needed a much… grander form."
It clicked. "You turned all of Hogwarts into your bloody Horcrux."
"Horcrux." He scoffed. "This is no mere Horcrux. This is the seat of a god."
"You're a lunatic." Harry said plainly. Riddle's eyes narrowed, flashing yellow. Ginny vanished.
"I gave her life, and I can take it away." Riddle said. "I hold life and death in the palm of my hand." His eyes drifted to Lily. "If the ability to make lightning is enough for an Asgardian to consider themselves a god, then I can claim the title as well."
Lily grunted and crumpled to the floor. Her hands fell away as red blossomed on her chest. She'd summoned a knife and stabbed herself before Riddle could dispatch her himself. He looked amused.
"Harry." She grunted. "I'm sorry."
"I know." Harry said. What else could he say? He couldn't forgive her.
"You don't… have to forgive me." She continued. "But please, don't hold it against your mum, your real mum. She didn't… make my mistakes."
"I won't." He told her.
"Fight like hell." She whispered. Then she died. With her last breath, a flame curled from her mouth. Harry's eyes went wide, understanding what Lily had just done. She'd been collecting magic throughout that battle, using the tattoos that patterned her body to store it. She'd used all that magic as kindling for Fiendfyre. The fire ate through her insides, consuming the stored magic before erupting to the surface.
"No!" Riddle spat. He vanished Lily's body, but it was too late. If Hogwarts held Voldemort's soul, purging the castle with Fiendfyre might actually kill him, and Riddle clearly knew it. The fire billowed out into the Great Hall, and Harry knew better than to stick around. He ran for one of the doors, but felt the ground tilt out from under him, the force of gravity shifted 90 degrees to pull him into the fire. He levitated himself up with magic, dodging a falling suit of armor as he entered a hall lined with portraits of Riddle in various landscapes.
A hand reached out from a portrait, completely shocking Harry as it snagged his ankle. Riddle's painted eyes glinted dangerously. "I need the Power Stone, Harry." He said. They both knew from Harry's memories of his battle with Thanos, that the Power Stone could be used to drain the magic from Fiendfyre, metaphorically starving it of oxygen.
Harry snorted. "Like hell." He brought the staff down on Riddle, creating a dent in his forehead that did not seem to impede him. Riddle responded with- what else!- a killing curse. The move was so predictable that Harry intercepted it the instant it left his wand, blowing up Riddle's hand. Harry kicked off, slipping from Riddle's grip. However another portrait Riddle had left its frame, and grabbed Harry from behind. With his wand at Harry's torso, he hissed out the killing curse. Harry's vibranium suit cracked as it absorbed the impact, but Shuri and Tony's nanobots rushed to fill in the damage. He had a massive stockpile of them in a hidden compartment enlarged by an extension charm, he could quite literally do this all day.
A sliver of his nanobots detached from his suit and rapped around this Riddle's neck, choking him out and pinning him to the wall. Fire burst through the doors, but Harry was snagged by more hands that materialized from the painting. He could easily escape; he could physically rip himself free or even flame out of the castle entirely and leave Riddle to his fate. He could let the fiendfyre rip through the magic-saturated castle like it was dry brush, but he needed the Soul Stone. Even if the fire destroyed it, Harry could recover it with the Time Stone, but he needed to find it before Death found him.
He needed to defeat Riddle just as much as Riddle needed to defeat him. They both held the tool of the other's salvation.
Neither can live while the other survives.
So Harry braced himself and kicked back into the portrait, slipping free from the slender hands that bound him. As he fell into the painting, the portrait hole seemed like a window to the outside world, and it was consumed in fire. Harry fell, the world a rush of colors and scene. He landed on his feet, in a grassy orchard that he vaguely remembered belonged to a painting on the fourth floor. Sure enough, Harry spotted another portrait hole staring out into a (so far) untouched corridor. He looked to the side, and saw an odd phase transition, to a winter village scene, and above was the bowl of fruit that acted as the entrance to the kitchens.
Harry didn't have long to ponder this- he supposed the portraits had to get around somehow- as he quickly spotted movement. Riddle was closing in on him from multiple directions. Harry wasn't going to wait to let himself get hemmed in. He leapt into another neighboring portrait- a room with a vase of flowers- dodging the curses Riddle's doppelganger sent his way and blasting the floor out from under him. Another doppelganger fell on Harry from above, and Harry flamed away, teleporting so that his fist was inside the chest of a third Riddle that was clambering into frame. That alone wasn't enough to kill him, so Harry used the power stone to channel a freezing charm into Riddle's body. Harry ripped his hand free, shattering the doppleganger, just in time to bat away a barrage of curses with his staff.
More Riddles joined the fray, and Harry weaved around them. He used acrobatics, the Time Stone and phoenix fire to avoid everything sent his way. One by one, he picked off the Riddle doppelgangers, usually with a spell that was grossly overpowered via infinity stone. He supposed it must have been a surreal sight to an onlooker- the canvas of the portrait littered was with painted bodies of the same man, with Harry- who was obviously not painted- in the center of it all.
A sectusempra amplified a dozen fold sliced clean through a Riddle's shield, then through his torso, then through the Riddle behind him and his shield, then through the wall, and through the tree in the next painting over, and on…
But despite the damage he could inflict, each portrait was resilient. The Riddle he'd just sliced dragged himself forward with one of his arms. The canvas bloomed with vibrant red as he pulled his torso along, pointing his wand up at Harry. "What are you going to do, bleed on me?" Harry taunted. He sent a barrage of blasting curses down at Riddle. That was the last straw for the floor, which gave way, dumping both of them into the portrait beneath them.
He landed on his feet, and caught sight of himself in the mirror. Dark cracks had opened on his skin, glimmering faintly purple. The Power Stone was taking its toll on him. "You're running out of time, Tom." Harry goaded, but he certainly was too. He had no idea how much longer his friends could hold Death back.
"Fine." Riddle's voice hissed in stereo. "We'll do this the hard way."
A new portrait hole opened in front of Harry, and fiendfyre billowed out. Harry leapt back to avoid it, but it raced out in all directions, leaving char in its wake. Harry ran, ducking through deserted landscape after deserted landscape. All the other occupants of the portraits had vanished, all that was left had been copies of Riddle, and he'd slaughtered them all. As he ran through a scene- a quaint cottage house- he spotted what he was looking for through the portrait hole. Harry leapt at the frame, and it vanished. Harry smiled grimly, that was just confirmation of his suspicion. Tapping in on the time stone, he reversed time a couple of seconds, and jumped through the frame, landing in the Room of Hidden things.
Where else in Hogwarts would Riddle hide something valuable?
"No!" Riddle shouted, the voice vibrating from the walls of the room, rattling Harry's chest. The door to the room exploded, letting loose a torrent of fire as this final sanctum was consumed. Harry created a small bubble of sanctuary around himself, draining out any fire that approached him with the Power Stone. Riddle screamed in pain.
Then Harry felt something stir, a warmth that began in his staff, quickly spreading down his arm to his chest, where it began to crest.
He smiled. They were going to win.
-----
Natasha did not know, could not comprehend that what occurred between Death and Dormamu. All she knew was that in the aftermath there was a black tear in the sky, and that Death was still standing. "Plan C!" She grunted, her voice scratchy. "Throw everything we've got at her!" 'Plan C' was the kitchen sink approach.
Loki conjured an illusion of Harry, making it grin tauntingly at Death. It was a clever distraction, but she saw right through it- sending a killing curse that toppled the frost giant. Thor howled in rage, hurling Stormbreaker at her. She caught it and sent the axe streaking back into Thor's chest with blinding speed. Pietro finally engaged her himself, weaving through curses and shrapnel to land lightning-fast punches on Hela's body, until Death's shadow snagged him. With every engagement, she neared the doors of the castle.
Carol landed at Natasha's side. "Do you need me?" She asked. Natasha knew how it ate at her to be excluded from the main action, but it was to her credit that she didn't go in guns blazing like the fighter jock she was.
"You can't." She said, watching as Skye gave her life to blast Death back a few feet. She winced and repeated to herself that it would all be worth it if they won. Then she saw Lily run headlong into the fight, and Natasha forgot all about the plan. "NO!"
-----
Neville stood over the dead basilisk, bloody sword in hand. Ironically, the artifact that he'd lost his eye trying to reclaim for wizard-kind had been in the Order's reach the whole time, if only someone worthy of it had tried. Ron had thrown himself at the basilisk to give Neville the opening he needed- classic Ron.
Fawkes alighted on top of the beast's head, trilling melodiously. Somehow, Neville felt his spirits pick up at the song. He sighed, scanning his surroundings. The stream of forces from the castle had dried up completely, but that was little solace. The Dementors had broken through, gliding towards the castle and swarming the pockets of witches that held out. He spotted Luna's hare patronus among the holdouts and made to rescue her. "Plan C!" He heard Natasha's voice crackle in his ear. That meant that they were out of options, and that Hela was on the brink of entering the castle.
Neville hated the idea of abandoning Luna (again, no matter how Harry and Luna insisted there was nothing he could have done about her imprisonment). Then he spotted three familiar figures fleeing the horde, and looked down to the sword. It wasn't his, no matter how long he had sought it or what he'd paid to get it. T'Chone had proven himself to be a true Gryffindor many times over.
And so, while Neville went to stand one last time with his friend, T'Chone charged into battle with Godric's sword. Fawkes trilled with satisfaction and disappeared in a puff of flame.
-----
Lily dodged the first killing curse sent her way, but the second curse blew out the ground beneath her feet. She was consumed by the explosion, but Septimius, who had charged in with her- was not. Instead, he was thrown forward, to Death's feet. Her shadowy hand flitted to him, but Natasha interposed herself between them, shielding him with her tao mandalas. Death took her instead, and it gave Septimius a moment to act. He grabbed her ankle, and Death froze, her mouth opening in a silent scream. Just as Natasha's protection had staved off her hand, Lily's final protection burned Death, giving the rest an opportunity to strike.
Rogue lunged to the ground beside Septimius, grabbing her other ankle. Finally, T'Chone plunged the sword of Gryffindor into her chest with a roar. The sword hissed and smoked against the goddess' flesh. For a moment, Death was still, and the three of them hoped that they might have actually stopped her.
Then she breathed in, and the breath left their lungs. Rogue, Septimius, and T'Chone slumped to the ground, comatose. Death staggered forward, ripping the sword from her chest and tossing it negligently to the ground. She had only one more foe in her way. Jean Grey stood between her and Hogwarts.
With a flicker of fire, Fawkes appeared on her shoulder. Jean closed her eyes and let fire consume her. She sent a torrent of plasma at Death, who used the Space Stone to cleave through it. The forest erupted in fire for miles behind them, while all near them- human, dementor, and inferi alike- were blown back. For several minutes, nothing could be seen. Fire consumed everything, the trees, the grass, the corpses.
Then, as suddenly as they had enveloped everything, the flames stopped. Death stood in front of Jean Grey, her shadowed hand plunged into her chest, gripping her heart. "Die." She hissed. Jean did not appear surprised as she fell to the ground. She had done her part, bought Harry time, and hopefully, left him with something more. She did not bother to speak to or taunt Death, she did not want to tip her off that anything was amiss. Her final words were spoken in her own mind, only Charles Xavier would hear them. We all did our best. It's up to Harry, now.
Death reached the steps of the castle. Paying no attention to Jean's body as it crumbled into ash. If she had, she would have noticed a featherless baby bird peak its head above the ashes- a phoenix reborn. Within the castle, a reborn power entered Harry, channeled through the feather in his Uru staff and into his body. At last, he was ready to face Death.
Hogwarts erupted in a pillar of fire that reached to the sky.