Obito really didn't mind burning a day by stalking a hero. The weather was nice, big screens everywhere were happily showing the Sports Festival wherever Ingenium stopped for a second, and snacks were easy to pick up at any corner store. Kei wasn't here, but she was keeping up a cover identity. And while Obito wasn't necessarily happy about it, he'd gotten used to not having Kei around for missions ever since February.

Off to Obito's left, Kakashi bit down on a sneeze as the two of them hopped across a gap between two rooftops, still following the silver-armored hero on his patrols. The local air was still weird.

If he was being honest, Obito half-expected this method of finding Stain to be as much of a bust as the scent-tracking. The Turbo Hero Ingenium was the leader of Team Idaten agency, and therefore he was one of the better-connected heroes in Hosu. If something did happen, he had a radio where Obito and Kakashi didn't, so he'd probably be on the scene of any crime as fast as he could. Therefore, Obito and Kakashi were saving themselves a tremendous amount of trouble stalking his various sidekicks by just following the big silver team coordinator around.

It helped that Ingenium's helmet made it difficult for him to cover his own blind spot. Someone probably ought to let him know.

…Just not until this tactic of last resort was fully explored.

Unfortunately, though they'd tracked down another police investigation, the victim was carted off to the hospital before Kakashi or Obito could Sharingan any answers out of them. The police had already trampled all over the site, making it useless for Kakashi's tracking technique. And to add salt to their collective wounded pride, Stain had apparently departed the scene via the sewer system. There was a lot Kakashi could do, both with his dogs and on his own, but all three of them had come to the sad conclusion that scent-tracking was just not going to work for this case.

Not that Kakashi would subject his dogs to city air if he could avoid it, but Obito understood. Some situations were a bit too complicated to have an easy solution. And even besides that, summoning techniques didn't appear to work on this side of Kamui.

Thus, stalking.

Not that Ingenium made it easy. Per Kei's explanation, this hero had engines built into his arms that helped him run faster or something. Obito didn't think it compared to shinobi speed, especially since he and Kakashi were some of the fastest people Konoha could throw at the problem, but he definitely took corners way faster than a normal person, and while blowing smoke everywhere. Because roof-hopping required a bit of foresight and Ingenium didn't seem to believe in slowing down except to make calls, Obito had been leading with his Sharingan ever since this mission started.

"Slow," Kakashi said, his gloved hand brushing against Obito's right shoulder. Sensation was a little dull in that side, but it was definitely a tap.

Obito shook the gleam of Ingenium's armor out of his eye before he dug his heels in properly. Rooftop gravel crunched under his feet as he skidded a bit, then turned to face Kakashi.

Kakashi jerked his masked head back and then down. Without any further words, he marched back over to the gap they'd just leapt over and dropped down with no ceremony. They'd found their Hero Killer, then, and Obito moved to follow.

At that point, the clank of light metal and rushing air met Obito's ears. Likewise, an armored shadow passed over him and, when Obito looked up, he spotted a silver figure careening overhead.

Ingenium landed in front of him, elbow pipe things jetting smoke. While his body was angled forward, as though expecting violence, his voice came out surprised. "You—you're a vigilante? Or a villain?"

Obito shrugged. He raised his right hand to scratch the back of his neck, feeling his face heat up under his mask. To salvage the situation, Obito almost mimicked Ingenium's voice right back at him just to make the awkward feeling fall on someone else for a change, but then steel met steel in the alleyway below.

Obito had already Kamui-warped from the roof to the ground before he even finished his master plan. Ingenium got a glimpse of a person spiraling away into a ribbony mirage, centered on the right eye of the mask, before Obito stepped out into a dingy alleyway.

"Wolf!" he barked, landing farthest from the street.

Kakashi didn't respond except to nod.

And from the shadow of a dumpster, the Hero Killer rose.

Taller than either Kakashi or Obito, but hunched as though his head was set a bit too far forward. His arms were bare under bandages running up to his biceps, balancing combat gear resembling cobbled ANBU gear. Obito noted the shift of shapes under his clothes and on belts, his Sharingan alerting him to dozens upon dozens of hidden knives, folding blades, and spare sharp objects. Heavy soles on already-modified shoes indicated yet more blades, perhaps spring-loaded. He was built like someone who fought for a living, complete with a damaged katana and ragged scarf to accompany the tails of his mask. His face was even flattened due to a total lack of nose, probably on purpose.

Stain looked like a jackass, was the point. It was a flexible word. Obito had picked up a few things here and there from Kei's vocabulary.

Between him and Kakashi, the Hero Killer was bracketed in by an ANBU agent and someone who had all the training and the power to sidestep attacks. Judging by the knife embedded in the brickwork, Kakashi had already deflected an attack or two with his kunai.

…If Stain had enough knives, this would be a very short fight.

Obito slid into a combat stance as Kakashi shifted his grip on his kunai. While both of them could have carried katana into this fight, Kakashi didn't need one and Obito could grow his own. Besides, that would have implied that either of them wanted anything to do with a fair fight with this jerk. If it was going to be a two-on-one beatdown, Obito would count it as a good day.

For a second, it was a standoff. Kakashi on one side, kunai held defensively in his left hand. Obito on Stain's other side, right hand flexing like he was going to go for—instead of grow—a weapon. Wood Release tendrils started to snake out from under his gauntlets, crawling down his leg and toward the nearest wall.

"More wannabe vigilantes trying to bring me to 'justice,' I see," Stain spat, drawing no more reaction than a cocked head from Obito. Seriously, what was this guy's deal? "Every time I kill you maggots, more just appear. You're not even worth dirtying my blade."

Across from Obito, Kakashi's Sharingan flashed noticeably, despite how he was backlit by the street. His right hand and arm lit up with white chakra lightning, running along gloved fingers like static.

Lightning Release: Stunning Flash. Obito knew that technique like the back of his hand.

Just like Kakashi knew his Wood Release moves, even if he couldn't copy them. Wood Release: Butterfly Net.

There were benefits to sending long-standing team members on serious missions together.

"The only thing worse than you are those fake heroes you keep dogging, like their fame will wear off on you," Stain went on, seemingly oblivious to the slowly rising tide of violence.

Then Ingenium hopped down from the rooftop, and the situation got needlessly complicated.

Now, Ingenium wasn't a bad guy as far as Obito knew. He rescued cats from trees, too, and he walked kids across the street sometimes. He organized people to do good. He seemed like a dependable hero. But he was also big, wore armor, and there was just not enough room in this alleyway for four combatants without getting in each other's way.

"Your reign of terror ends here, Hero Killer!" Ingenium squared his stance and raised his fists.

"No…" And Stain's flat face turned toward Ingenium. "It's just getting started."

Obito held out his free hand, snapped his fingers to get Stain's attention, and made a gesture that left little to the imagination regarding his opinion of the Hero Killer's self-satisfied ranting.

This did not meet with approval. While Kakashi clearly rolled his eyes based on how his Sharingan light blinked out for a second, Ingenium coughed. Then Stain hissed, "You'll die first."

Obito said, in Stain's voice, "Come at me, bro." And just to make the moment complete, he added a mocking "come here" motion with his left hand.

Stain lashed out at speeds nearly comparable to a tetchy chūnin, but Obito's Mangekyō Sharingan slowed the entire world to a crawl. While Obito grinned under his mask, Kamui shifted along with the slash of Stain's ragged-edged katana as it seemingly sliced him open from shoulder to opposite hip with no resistance.

"No—" Ingenium began as Obito flopped forward onto the ground, only just avoiding cracking his mask on impact.

Or so the two Tokyo-natives seemed to think.

Stain lifted his blade and then stopped dead. Just as he realized the broken steel was still clean, Stain tried a follow-up attack that stabbed downward through Obito's head.

To exactly as little effect as before.

"Nice try, asshole," Obito said, still in Stain's voice. He stepped back, watching the man's eyes widen. "You're just too slow."

Kakashi was too professional to sigh, but it was a close thing. Instead, Obito heard him say, "Ingenium, you're in the way."

"As useful as his Quirk is," Ingenium noted, not taking his attention from Stain, "arrests are Hero work. I can't let you two handle Stain on your own, no matter what."

"Your call," Obito chirped. Given the funny look everyone gave him, he imagined no one quite expected to hear a cute, piping voice coming from behind his eerie white mask. He stalked behind Stain, putting his hand up against the Wood Release web he'd already started. "But you should still back up, say, fifteen meters."

Ingenium didn't, probably because Stain went for him next. A knife flew and struck one of the places where his armor didn't cover his undersuit, slicing through his tricep on its way to the street.

The hero staggered two steps back with a shout of pain—

Kakashi's arm lit up until it was nearly blinding—

Stain leapt for Ingenium's throat, katana curved in a lethal upward arc—

Obito slammed his chakra into his right arm just as a knife whipped out of nowhere and hit him square in the right shoulder. It bit into muscle, but couldn't touch bone even if slammed home with Tsunade's strength—his Zetsu arm didn't have any bones to break. And the pain was only about as bad as a sharp slap. Getting Kamui up first was more important, and his Mangekyō ached again to let him know that was a great plan.

—Obito's Wood Release vines snaked up from the ground and hardened to something akin to steel bars, blocking Stain from reaching Ingenium as though a door had just been slammed in his face—

—Stain's tongue slipped through the bars and caught a drop of flying blood—

—Ingenium hit the ground with a thud—

—and Kakashi's lightning arced out directly for the man carrying the most steel, engulfing the alleyway in white light. Bolts passed through Obito like nothing, making his fingertips tingle.

Obito was pretty sure, after the fact, that he saw his own retina from the flash. He would give Kakashi a thorough ribbing for that later. As he blinked the red out of his vision, he took in the scene.

Stain was upright only because Obito's Wood Release had made a sort of Hashirama tree in the middle of the alley, and it was awful hard to pry anybody out of the wood without a much heavier weapon than Stain's sword. They'd be chopping him out with an axe, and hopefully with a lot of heroes making sure he wouldn't stab anybody again.

Speaking of, it'd probably be easier to be sure of that if Obito stole all his goddamn knives for the police to process. Still, Obito glanced around to be sure his two fellow fighters were all right.

Kakashi crouched over Ingenium, peeling back a layer of undersuit to check on the injury. He'd made a heavy bandage out of gauze and some medical tape, and folded it even as he kept his Sharingan trained on the wound. Then, "It's not deep. Can you keep pressure on it?"

"I would if I could." Ingenium's voice was about half an octave higher than usual. "But I can't—I can't move. At all."

"Huh," said Kakashi, and then pressed the pad to the injury as he levered the hero's arm up and above his heart. "Quirk?"

"Probably." Ingenium groaned quietly, wincing noticeably even with his full-face helmet as Kakashi worked. "Are both of you all right?"

Kakashi nodded.

Obito idly pitched two combat knives over his shoulder. They clattered to the concrete. "Yep."

"Good." Kakashi helped Ingenium sit up, still clamping his hand over the wound. "My communicator is in my helmet. Any chance you could help me reach it."

"The two of us are outta here the second your sidekicks show up," Obito warned, kicking a multitool toward the dumpster. He jabbed a thumb at the still-unconscious Stain. "He's going to jail on his own."

Ingenium's helmet canted to the left. "You think I'd try to get you arrested for vigilantism?"

"…Yes?" Obito replied, finally turning away from the Hero Killer. He'd get out of there when someone helped him, not before. "I mean, it's in all the pamphlets."

"If I'd tried taking him on alone, I'd probably have died," Ingenium explained. He still couldn't move, apparently, but Kakashi was being patient about the whole thing. "I don't think the police would agree, but it's a hero's job to keep innocent people safe even if it costs us everything. Sometimes, that includes legal protection."

"Oh." Obito scratched the back of his head, and then remembered he was wearing a full head covering and it was than less effective. "Uh, that's actually nice of you to say. Wolf, maybe if we make sure the paralysis wears off first…?"

Kakashi sighed. "Make your call, Ingenium. Stain isn't any more arrested than he was a minute ago."

Ingenium managed a pained laugh, now that his adrenaline rush was starting to wear off from lack of use. "All right, all right."

Ingenium got his full movement back (or nearly) a little before his now-alerted sidekicks started converging for real. He was going to be mobbed by worried heroes and carted off to the hospital soon, apparently. Once they were all sure Stain's Quirk had worn off and the guy still wouldn't be going anywhere, Kakashi let Ingenium take over caring for his own injury before disappearing ahead of police sirens.

By that point, Obito had managed to wheedle a masked selfie out of the hapless hero—because of course he had to. Ingenium seemed more baffled than annoyed, probably by how quickly events had progressed, and obliged. With a cheery salute, Obito vanished up the wall like a spider caught in the light, leaving the police and pro heroes to deal with the serial killer. He could send photographic evidence to Kei about their successful mission, so she'd finally stop worrying.

He sent it immediately after he and Kakashi were both out of sight and away from any of the swarming heroes. So: ten blocks away.

It took until a couple minutes later, when he went to change into civilian clothes inside Kamui, that he remembered Stain's knife was still sticking out of his shoulder.

Kakashi facepalmed hard enough to put Kei to shame.