Disclaimer: Being neither British nor Japanese, it should therefore come as no surprise that I own neither Harry Potter nor Naruto, nor anything from their respective franchises.
In the next room, his back to the door, stood Quirinus Quirrell, muttering to himself and looking at his reflection in what Iruka recognized as the Mirror of Erised. The instant Iruka moved towards him, however, Quirrell snapped his fingers and the chuunin found himself suddenly cocooned shoulders-to-ankles in black ropes. "I had hoped that I wouldn't have to dispose of you." The man spoke coldly, firmly, with none of his usual stutter or quiver. "Such new and interesting magics you brought, but I cannot abide interference... or witnesses."
Iruka glared coldly back at his newest treacherous colleague. "What I can't abide is people trying to murder my students."
Quirrell smirked darkly. "Ah, so you noticed my little ploy during the Quidditch game, did you? It was risky, really, far too great a chance of exposure, but we all do what we must. Now, as much as I'd love to engage in some spirited intellectual discourse with you, I am rather busy at the moment." With that, he waved his wand and Iruka found himself unable to make a sound.
As Quirrell's attention returned to the mirror, Iruka immediately tried to free himself. Unfortunately, no matter how he moved, the magically conjured ropes kept him bound tightly, unable to even reach any of his weapons. Wrapped this effectively and comprehensively, he couldn't even Substitute his way out, though given the fact that Quirrell and the Mirror were the only items of appropriate size in the room, that would have qualified as a 'high-risk' strategy anyway.
Iruka watched as the traitorous Defense Professor continued to study the Mirror. He would stare at his reflection, examine various details of the frame, walk around to check the back, and occasionally draw his wand to cast various spells. All the while, he continued to mutter to himself. What had Iruka edging towards panic was when a high, cold voice answered. It was looking increasingly certain that the supposedly-late Lord Voldemort was involved; which left an important question: Was this some form of remote communication, or was he in the room somehow?
After many tense minutes of watching Quirrell grow progressively more frustrated, Iruka heard the sound of soft footsteps, far too quiet for the turbaned traitor to hear even if he weren't muttering distractedly. Finally, backup! It was only as they got closer that the chuunin realized that the weight and rhythm of the footfalls weren't those of an adult; given the fact that there was only one student who had reason to come here and the ability to go unseen, it was a pretty safe bet who this was.
Making sure that Quirrell was otherwise occupied, Iruka looked straight at where he sensed his student. 'Run, Harry!' Being silenced, he could only hope that the young Potter could read his lips. Whether he could or not, though, his approach only briefly hesitated. A soft rustling of cloth heralded the appearance of a small hand awkwardly holding a shuriken, which was quickly put to work sawing at the magical bindings. Resigned that he couldn't convince the child to flee to safety, Iruka instead wriggled into a position that he hoped would hide the hand from Quirrell's view.
Luck, it would seem, was not on their side that night. "Who's there?!" The hoarse shout came from Quirrell's position but not in his voice. As he swiftly rounded the Mirror, the man's wand flicked and a blast of wind blew Harry's cloak from his shoulders and off into the corner of the room. Another quick wand motion and the student joined his teacher bound on the floor, his appropriated shuriken falling uselessly flat behind Iruka.
"Ah, Harry Potter, of course." Quirrell smiled mockingly. "How kind of you to come; I had feared that I might have to leave that bit of business unfinished. And you even bring me a gift! This cloak will certainly come in handy later; I'll be able to feed you both to Hagrid's beast and then leave unseen, with no-one the wiser. For now, though..." He turned back to the Mirror, continuing his examination. "I don't understand... is the stone inside the mirror? Should I break it? What does this mirror do? How does it work? Help me, Master!"
The other voice replied. "Use the boy... Use the boy..."
A clap of Quirrell's hands had Harry free, before he ordered the young Gryffindor to stand before the mirror and describe what he saw. He was so focused on the mirror that he clearly missed the subtle tug of Harry's robes, as if something heavy had been dropped into his pocket. Iruka's rapidly-escalating panic wasn't helped by his student's frankly pathetic attempt at a lie, and that was before, at the voice's urging, Quirrell began unwrapping his turban. When he turned around, the second face on the back of his head fixed its red-eyed ophidian stare on Harry.
After a brief monologue that was half cryptic, half informative, and all melodramatic, the now-confirmed Voldemort demanded the Stone from Harry's pocket. Some fairly textbook attempts at intimidation and psychological warfare later, a now enraged Harry glanced briefly at Iruka before darting for the exit with Quirrellmort in pursuit. The moment Quirrell's hand seized the boy's wrist, however, both shrieked in pain and Iruka could swear he heard a soft sizzling sound. Harry quickly broke the hold on his wrist (if they survived, Iruka would praise him for flawlessly executing the basic taijutsu move) and both combatants retreated several steps, both still clearly in pain. Quirrell was actually hunched over, cradling a hand that was clearly burned and blistering.
Commanded by his master, Quirrell attacked again, bearing Harry to the ground under his weight and wrapping both hands around the boy's throat, screaming in pain as he did so. Another textbook hold-breaking technique later and the possessed man was again retreating, both hands now severely burned. At his master's order, Quirrell raised his hand to cast a presumably lethal curse, but Harry was faster. He leaned forward, grabbing his opponent's raised hand with his own and pushing it away while his other hand reached for the man's face. The screams this time were of an even higher pitch and intensity, largely drowning out Voldemort's furious shrieking, but Harry himself was clearly hurting a great deal as well. Quirrell tried to roll away, but his intended victim kept hold of him, maintaining contact even as his own strength visibly waned.
Iruka's heart soared when Albus Dumbledore strode through the black flames, his face a mix of concern and righteous fury. A barrage of spells blasted Quirrell away from Harry, sent his wand flying from his pocket, and left him bound, unconscious, and likely incapacitated in a few other ways as well. As the Headmaster ran to his fallen student, an oily black mist streamed out of Quirrell. Dumbledore fired off several spells into the cloud, but they seemed to have no effect as it fled shrieking through the wall.
Headmaster Dumbledore's attention immediately returned to Harry, frantically casting diagnostic spells for several seconds before sighing in relief. "Just exhausted," he said as he Vanished Iruka's bonds and canceled the silencing spell, "but it was a close-run thing." After Summoning the Stone from Harry's pocket, he rose and moved over to Quirrell's still form, casting more spells. "It would appear that Quirinus was not so fortunate. Possession exacts a terrible toll on the body, which would explain his resorting to unicorn blood, and without the Elixir of Life it is doubtful that he could have survived the wraith's departure even without such grievous wounds." Now the aged wizard seemed to scrutinize the late Professor. "I have my suspicions, but I must ask you while hoping they are wrong: Was it Lord Voldemort possessing him?"
"That's what he claimed," Iruka replied as he crouched by his unconscious student, performing some basic first-aid checks. "I actually came down here after him because Harry's scar started hurting, and he said it'd been hurting on occasion since the Sorting. It reminded me of something from back home, a mark that a notorious criminal would place on prospective followers; he could use it to inflict pain on them when he was near, and twice he used it to cheat death. That set me worrying that Voldemort wasn't as dead as most hoped, and that Quirrell wasn't just seeking the Stone for himself."
"Perhaps we might continue this conversation after delivering Mister Potter to the care of Madam Pomfrey?" Dumbledore gestured towards the black flames, before heading for the door. Iruka nodded, gently lifting Harry's insensate form and following. They stopped in the potions room to sip from the 'return' bottle and spell some of its potion into Harry's stomach, and grabbed a pair of brooms from the key room to make their way back up the shaft to the third floor. As they walked, Iruka recounted his and subsequently Harry's encounters with Quirrell and his passenger.
"It was incredibly foolhardy of Harry to come after me like that." Iruka looked down at the unconscious first-year in his arms. "It was also incredibly brave and incredibly lucky. If it weren't for him, I might not have made it out of there alive, and you might have found yourself facing a restored Voldemort. He showed why the Sorting Hat put him in Gryffindor tonight. True, he froze at first, but that's pretty common the first time somebody is in that kind of danger." He chuckled ruefully. "Even the current leader of Konoha, one of the greatest heroes in our history, froze up like that. Once he started acting, though, he kept his head. I could see it in his eyes when he tried to run that he was hoping to lure Quirrell away from me while I was helpless, and when he had to fight he refused to give up despite the pain he was in. I just wish it hadn't been necessary, that I hadn't let Quirrell catch me flat-footed like that."
"Even the best of victories leave us with regrets," Dumbledore commiserated, "but I cannot help but think of how tremendously proud James and Lily would be of their son, even if at the moment it would be overridden by worry."
Upon entering the Hospital Wing, Iruka saw his other two students were already present. Neville was lying in one of the beds, whether asleep or unconscious he couldn't tell, while Hermione had leapt from her seat nearby to rush over to the newcomers as soon as she saw them. "Harry!" Her shout was loud enough to draw Madam Pomfrey bustling form her office. "Is he all right, Professor? Are you all right? What happened to Professor Quirrell? Is the Stone safe?" As usual for Hermione, her excitement caused her to fire off a stream of questions at high speed without waiting for answers.
It seemed that rescuing Iruka was in fashion that evening, as Madam Pomfrey spoke first. "Miss Granger!" Her scolding admonition was much quieter than the girl's inquiries. "Kindly refrain from disturbing Mister Longbottom's much-needed rest!" Chastised, Hermione withdrew with a sheepish expression. "Now, it would seem I have another patient. Please set him down here, Professor." She indicated a nearby bed. Iruka, knowing better than to tempt the ire of a medic in any world, promptly complied.
Several scans later, the Healer nodded. "Magical exhaustion, and as severe as I've seen it in a student. Dare I ask how this came about? No, no I thought not. Regardless, Mister Potter is well enough otherwise. I'll need to scan him again in the morning to confirm the timing, but for now I'd say that he should be awake in two to three days. He'll need to stay at least another day or two after that for further rest and monitoring, but after that he should make a full recovery. Now, unless you're expecting any more casualties to come through my door tonight, it is past time for all of us to seek our beds."
"Of course, Poppy." Headmaster Dumbledore turned to Iruka. "Professor, would you be so good as to escort Miss Granger back to Gryffindor Tower? I'm afraid that my role in handling tonight's excitement is far from over, but it would ease my mind to be certain that all our students are accounted for."
"Of course, Headmaster." Iruka tipped his head to his employer before addressing Hermione. "Shall we?"
Once they were out of earshot of the Hospital Wing and the departing Headmaster, Iruka spoke again. "The Stone is safe, and Quirrell is no longer a danger to anyone. As for me, the only injury I took tonight was to my pride, something I intend to fix as soon as possible. Beyond that, I'd prefer to wait until I can speak to all three of you to share any details, though I will be hearing how I ended up with a first-year student backing me up instead of a trained adult. That can wait too, though; for now, we all need to rest and recover from one frantic evening."
A/N: Sorry for the somewhat (~6-10 hours) late posting! My routine got thrown off a little, which led to distraction. Also, apologies for the relatively short chapter, but as I've said before I try to break them where it makes the most sense to me.
Yes, Iruka got his arse kicked. He underestimated his opponent and didn't have enough knowledge about magic. Now, however, he realizes this, which means he's less likely to make the first mistake and can start working on fixing the second. Both S.E.N.'s training and Iruka's own are going to change as a result of this (which is a big part of why I had things shake out the way I did, the other major reason being that Iruka stealth-ganking Quirrelmort would be boring and anticlimactic). I will admit that this was one of the very few places in the story where I've actively steered events rather than just letting the characters do whatever makes the most sense at the time.
Regarding Harry breaking Quirrelmort's holds, both sets of martial arts classes I've taken taught numerous responses to being grabbed by one or both wrists. Part of my takeaway from this (other than learning the techniques) was that grabbing the wrist of a trained martial artist is at best unproductive and at worst a recipe for pain (unless perhaps you're at least comparably well-trained). The more practically-oriented classes also included a couple of responses to manual choking. Given that both are part of mundane self-defense courses, it made sense to me that they'd be part of what limited taijutsu Iruka has taught to S.E.N. (and Luna) thus far.
Voldemort's wraith didn't fly through Harry because I'm going by the book version of events, in which Harry simply passed out from the strain. Also, there's no way to state this in-story, but Harry will be waking up a few hours earlier than in canon because his training with Iruka has slightly strengthened his magic and more noticeably strengthened his body.
EDIT: Apparently some people aren't getting their alert emails, and one such suggested I point this out in case others are affected and haven't yet noticed. This seems to happen on occasion on ffnet, and is rather frustrating. On the plus side, you know at least approximately (very approximate this chapter, I'll admit) when I update.
Fic Recommendation: "The Cupboard Series 1: The Cupboard Under the Stairs" by Stargon1 - first in a long series of fics (as you may have guessed from the title), it has a Harry that's somewhat less unaffected by his 'upbringing', though not nearly to the degree of "Brutal Harry". The entire series has concluded, and is well worth the read.
Posted 11 February 2018
Current WIP Chapter: 52 (Currently a bit stalled while planning future plot details)
Edited 6 June 2018: The Cloak of Invisibility is non-summonable, apparently. This is now accounted for.
Current WIP Chapter: 61
Edited 15 July 2018: Made it clearer that Iruka was wrapped up thoroughly, so he can't just kick his way out of the problem, thanks to a review from user "iluvstorys".
Current WIP Chapter: 63