Timeline clarification:
The following does not take place in current DC canon. It's not pre-crisis, either, instead a strange amalgam of eras. Hal Jordan is the Green Lantern, Jay Garrick is the Flash, it's modern day, Superman and Batman are both fresh on the scene.
Now that that's cleared up, on to the story.
Faster than a speeding bullet, Superman flew across the Appalachians, heading east from Metropolis around mach 6. Ahead, somewhere behind the swiftly approaching terminator line, was his destination: Gotham.
The small lead box in his hand would normally have caused no more exertion in him than a feather, but the few bare inches of dense metal just wasn't enough to shield him from the harmful effects of what lay inside…
Into the night he flew, the sun setting somewhere past Pennsylvania, New York was just a dark blur, the rapidly approaching Miskatonic River twisted like a worm through the dark valley that lead to Gotham…
Superman slowed dramatically to slightly less than sound as he dipped beneath the dark trees in the forests far outside Gotham. Ahead, his piercing gaze caught sight of a great emptiness in the earth. He lowered, until he was skimming along a few feet above the ground. Ahead, a dark unpaved road stopped dead at a blank cliff face.
Superman flew through it.
Bruce Wayne, the Batman, sat in his bat-cave, eating some chowder. He had just come down after catching the news upstairs. After making some notes on the stock market and asking Harriet to drive Dick to a basketball game, Bruce had taken off his shirt, put on his light pants, and settled in to check out the real news via his massive super-computer. Thirty LCD screens arrayed before him described riots in Kahndaq, an official at Akrham being hospitalized (Joker-related poisoning, of course, Bruce would have to look into that tonight), DA Dawes again debating with Chief Yindel about the legitimacy of the Batman… slow news day.
Except for this bit out of Metropolis… reporter Tana Moon, in a Wayne Broadcasting chopper, hovering over Interstate 135, where lay…
Boom!
Bruce coughed a bit and set down his coffee, looking up in surprise.
Softly, Clark Kent, the Superman, descended from the darkness of the bat-cave.
Bruce Wayne nodded at the man of steel. "To what do I owe this intrusion, Superman?" He smirked.
Clark walked over and sat down in Robin's chair at the vast computer console, next to Bruce. He leaned forward on his knees and sighed.
"I just had Lex arrested again."
"I saw," Bruce responded, nodding at the main screen on the console. A stout robot the height of a small skyscraper was laying in tatters along the interstate. It had landed there when Superman threw it from downtown Metropolis, reporter Tana Moon explained. A number of SWAT vans and police cruisers were parked alongside the fallen robotic warrior, as well as a few ambulances. Notably, one screen had a frozen image of a bald man, handcuffed, sitting on the back of an ambulance while medics checked his bruises.
"He… he had something," Clark continued, his fingers running along the thick lead box in his hands. Bruce looked at the box, and noticed that Clark's hand looked like he was gripping the box with all his might. His hands were completely flushed white.
"I… until today, I'd never really realized how much power I could bring to a fight. I mean… Bizarro's just mind games, and sure I've held up trains and buildings and such before… but when I threw that giant robot two miles…" Clark looked up at Bruce, "Two miles. Jesus Christ. It was like throwing a fastball, that's all.
"It got me thinking. Lex is always saying that I'm dangerous, that I could be set off at any moment… I never gave it any thought before, because who wants to worry about going crazy… god, Bruce, I could hurt people if I lost it, I could…"
Clark looked down in shame, shaken. Bruce was uncomfortable in the silence, glancing up at the screen. The red hues of sunset began to melt into the limitless orange glow of the background. It was so serene, and wasn't at all an awkward moment with a friend.
After a moment, Clark thrust the lead box into Bruce's hands forcefully. Bruce took it from him graciously, noting how the color began to return to Clark's hands as he pulled them away.
"Lois… got this off him. He was wearing it in the robot. She hit him over the head with a wrench, took it off him, and got out of the robot before I threw it. I don't… I don't know where he got it, I thought I'd managed to throw all that stuff to Mars, but maybe I missed some or…"
Clark stopped talking and clasped his hands together, looking up at the screens as Bruce opened the lead box carefully, already knowing in his heart what was in it.
It was a ring. A green ring. A brilliantly glowing green ring, with the letters "LL" engraved into it. Not at all like Hal's power ring, instead more like a thick wedding band.
"I want you to have it, Bruce."
"I'm sorry, Clark, but I'm happy with my life as a bachelor," Bruce joked slightly, trying to cheer up his friend.
Clark looked up, a strained smile on his face. "I'm serious. I realized today… that… I'm dangerous. If something goes wrong, if I can't see how my actions are adversely affecting the world, if it gets to the point where I need to be… well, I just can't trust Hal or Batson or Garrick with the decision. I trust them, in general, but for… for this… I need you."
Bruce closed the lead box and put it on the far end of the console from Clark.
"I… I trust you. You'd know what to do, how far was too far… God, what am I even talking about…" Clark buried his head in his hands, sighing.
Bruce grimaced, then awkwardly extended his hand and… sorta patted Clark on the shoulder. "Um… it's okay, really. I understand what you're asking of me, and… it's a great honor to be given this responsibility."
Clark looked up and smiled at Bruce. "Really?"
"Of course. You can trust me, Clark," Bruce said, shaking hands with the Man of Steel.
Clark smiled, the warmth from Bruce's hand easing the ache in his own. "Thank you, Bruce… really, thank you so much, I, I just can't-"
"You won't ever have to," Bruce cut in, smiling warmly. He stood up, and after a moment Clark followed suit.
"Go home, Clark, and tell Lois you love her, or whatever," Bruce said, smirking.
Clark grinned and chuckled, "Really, this is just… such a load off, Bruce, you don't even know."
"Relax, don't worry about it, Clark," Bruce responded.
Clark nodded, then kicked into the air. He floated up about seven feet, stopped, and looked down at Bruce. "If there's ever anything you need…"
"Oh, I'm sure I'll think of something sometime."
Clark nodded, then flew out of the bat-cave, probably knocking another hole through the façade of the cliff-face out front. Bruce winced, but it would be simple enough to fix.
He nervously crackled his knuckles and turned to the lead box on the computer console. He breathed deeply, then walked over to the lead box and opened it.
He pulled out the ring.
It was just a tiny thing, a simple piece of forged alien metal. Idly, he tried it on his ring finger, but it was a bit big. He could fix that later, he figured, and maybe score off the "LL".
Bruce placed the ring back in box, and snapped it shut, then sat down at the computer and pressed the intercom button.
"Alfred?"
"Yes, Master Wayne?"
"I need to know if LexCorp's been buying up land in Smallville, been sending up any new satellites, anything he could use as cover to try and find Kryptonite. And also have one of our moles check into any possibility he's been trying to synthesize it again."
"I'll get right on it, sir."
"Oh, and…" Bruce's face darkened as he pulled back a bit into the shadows… his gaze fell upon the radar screen… a small, humanoid-sized bogey had just left the Miskatonic valley… probably out of ear-shot by now.
"… And have Fox run a fresh round of background checks on anyone who's even heard of our operations up in Alaska."
"Of course, Sir."
"Thank you, Alfred."
Bruce lifted his finger from the intercom and looked up at the vast array of computer screens. A sleek red figure zipped silently through Keystone city, thunderstorms in Fawcette, and another daring rescue in Coast City by the Green Lantern.
Another fine day in heroics.
Bruce stood up and picked up the case the ring was in, walking away from his computer and into the darker, deeper sections of the batcave.
A few dozens flights of roughly hewn steps downward later, Bruce came to an enormous lead lined steel door. He typed in a string of random numbers and letters, then pulled open the door, hydraulic hinges aiding the lumbering process.
Bruce stepped into the vault, unmarked and unlabelled on the outside, but what Bruce would mentally re-affirm as his "Super-closet".
He walked down a row of lockers to a labeled one near the end. He typed another combination on the keypad installed on the locker, springing it open. Gently, Bruce placed the case containing the kryptonite ring on a small shelf on the left side of the locker.
Taking up the center was a vast steel power-suit, two wickedly sharp and long antennae forming the ears on this humongous batsuit. The lead-lined steel faceplate prevented any x-ray heat vision from giving the wearer impromptu lobotomies, and similar precautions were taken on most of the rest of the powerful armor.
At the wrists, three long and serrated titanium claws, edges impregnated with potently glowing kryptonite, extended outward over a heavy liquid-cable grappling hook launcher. Two large bandoliers, laden with tear-gas grenades (each containing light kryptonite shavings to spread out in a great green cloud) hung next to the suit, as well as a powerful if somewhat inefficient jetpack. He'd not yet managed to develop the anti-gravity generators, but when he did this suit was the first place they'd be installed.
He looked at the chest of the suit of armor. In place of the classic bat-symbol he'd installed a powerful red-sunlight lamp shaped… well, like the bat-symbol. If his opponent was conscious of his actions, Batman reasoned, the re-affirmation of himself as Batman, Superman's friend, might give him the edge needed to take Clark down.
And, if the opponent was just some other Kryptonian… well, they'd learn to respect and fear the bat as well.
Batman closed the door to the locker, chiding himself for the lateness of the hour. 5:30 already, and still he wasn't on the streets. Hopefully, he wouldn't have to call Grayson in… the boy deserved to have at least a chance of a normal public life, if for no other reason than to assuage public suspicion.
The label above the locker read, simply, "Superman".
Batman then walked out of the vault, past all the other labeled lockers.
"Wonder Woman", "Flash", "Marvel", "Green Lantern", "Aquaman", "Martian Manhunter", and "Plastic Man".
The Batman closed the vault door, locking it, and went to put on his more mundane crime fighting gear.