Here is how I think the alternate version of the ending should go. I made the Overlord's plan more devious so the heroes wouldn't need to be so trusting. Their breasts are still turning to high explosive, but the ending changes because they call for help instead of just ripping each other to pieces.
Hyperbunny dropped the destabilizer gun to the floor and pulled her suit down to expose her breasts. She frantically rubbed her skin, trying to wipe away the glowing green liquid even as it sizzled and absorbed into her skin.
"Oh shit! No, no, no! What is this stuff? What did you do to me?" screamed Hyperbunny, still clutching her breasts.
Novahawk laughed and grinned as she sat up, ignoring her cuts, her green eyes gleaming with satisfaction as she stared at Hyperbunny's bare breasts.
"I got you. You're going to lose those ridiculous balloons! The chemical will shrink your tits to half their size."
Hyperbunny's mouth dropped open and she fell to her knees. Her big blue eyes widened and filled with tears. "You... You bitch! No! This can't be happening!"
"Believe it!" Novahawk rolled her head back and burst out laughing, slapping her knee and cackling wildly. "This is exactly what you deserve for almost taking my team from me!"
"Yeah?" Hyperbunny sniffled and wiped the tears from her eyes. "Well... Well... If it shrinks my tits by half, that must mean you'll be flat as a desk!"
Novahawk's laughter cut off instantly. She scowled and looked down at her chest. She grabbed her breasts and scrambled to her feet. She glanced around frantically, then suddenly smirked.
"Sorry, Bunny, but you're the only one losing her breasts today. I'll just get the antidote."
"There's an antidote?"
"Not for you, there isn't." Novahawk activated her communicator and said, "Call Lightyear Labs. Connect me to Harold on a top priority encrypted channel."
"Novahawk! I've been trying to reach you!" came a frantic voice from the communicator.
"Shut up, Harold! Not now. This is an emergency," snapped Novahawk, "I need an antidote for the breast shrinker. I got some on my breasts. You've got to neutralize it before it takes effect."
"Oh no! Novahawk, it's not a breast shrinker! The Overlord somehow figured out what we were doing and changed the formula."
"What? That's impossible! How could you let that happen?"
"It will convert your breasts to high explosives and kill everyone! There's no time for you to get to the lab. You could explode any minute!"
Novahawk's face went pale and she swallowed heavily as she slowly turned to stare at Hyperbunny. The young hero had tears running down her cheeks and she sobbed softly as she clutched her breasts.
"This... This is all some sort of joke on the new girl, right?" Hyperbunny's voice was weak and trembling. "My tits aren't really going to explode, are they?"
Novahawk gasped as her breasts suddenly started to swell, bulging forward and pushing out between the laces of her suit. More of her bare skin was pushing out the side of her suit as her breasts grew.
"Damn it! It's already happening! No, not yet! My breasts!" Novahawk fumbled to press her communicator. "Everyone get to the vault! Our breasts are going to explode! We need help now!"
Novahawk blinked away tears and growled to herself. "Fuck you, Harold. If I lose my beautiful breasts because of this, I'm going to rip your nuts off."
Laserforce flew into the vault in a blaze of blue light. The crystal in his bare, muscular chest flared bright blue and then bubbles of blue light surrounded Novahawk and Hyperbunny.
"I'll try to contain the explosion in a light shield!"
"Damn it! I need you to stop my breasts from exploding, you fool!"
With a hard groan, Novahawk bent forward and shuddered. Her laces twanged as they snapped. Her bare breasts sprang forward out of her costume, veins bulging, green fluid leaking out of her swollen nipples. Novahawk clutched her breasts with both hands and wailed.
"No! Not yet! Help me!"
Dr. Electrode ran into the room. She was a slender woman dressed in a skin-tight black suit that covered every inch of her body, even her mouth and eyes. It clung so close to her skin that it cupped each of her modest breasts, showed the points of her nipples, and conformed to every detail of her vulva.
She raised her hands and her electronic gloves sent scanning beams to Novahawk's breasts and Hyperbunny's breasts.
"Oh no," whispered Dr. Electrode, "They both really are going to explode, and it will destroy this entire base. I don't know if your shields are strong enough to stop it, Laserforce."
"Fix it!" snarled Novahawk as she struggled to hold up her still expanding breasts, "I can't take much more! You've got to save my breasts! That's an order!"
"I don't know!" yelled Dr. Electrode, "There's no time! I need time to think!"
"Allow me!" said Dr. Roboto as he hurried into the room carrying a steel pressure cylinder. "My electronic brain has analyzed your scans, Dr. Electrode. Pardon the eavesdropping, but this has a 97.6% chance of neutralizing the explosive."
The cylinder weighed 500 pounds but Dr. Roboto was a man covered in shiny polished steel and he held the massive cylinder in one hand. He stared at Novahawk's breasts with glowing electric eyes and aimed the nozzle at her chest.
"Do it!" groaned Novahawk through clenched teeth, "Do it now!"
"Drop the shield!"
A rush of white mist blasted Novahawk's chest and she howled in pain. Her back arched and her powerful muscles tensed all over as she squeezed her eyes shut and let the gas rush across her tightly swollen breasts.
"Is it over?" panted Novahawk, "Did it work? The pain is gone, but they're still... My breasts are still so big."
She reached up to cautiously touch the bleached white skin of her giant breasts. Dr. Electrode's scanning beam sweep across her again.
"Yes, it worked. Most of the explosive has been neutralized, and the rest will be harmlessly absorbed by Novahawk's body."
"But what's happened to my breasts? They feel so numb and they're covered in something hard. It's like stone."
Dr. Electrode frowned. "I'm sorry, Novahawk, but the explosive has been chemically converted to mostly calcium carbonate."
"What!" Novahawk gaped and clutched her breasts. Thin streams of white powder started to flow between her fingers to pile on the floor. "What does that mean? There's a way to fix this, right?"
"It's impossible. There's nothing living in your breasts anymore. I'm very sorry, Novahawk, but at least the explosion has been stopped."
"No! Help me! They're... They're falling apart! Help! Somebody!"
Novahawk fell to her knees and chunks of her breasts broke away in her hands, shattering when they hit the floor. She clutched at the dust, collecting in handfuls and trying to press it back against her chest.
"No! This can't be happening!" Tears ran down Novahawk's cheeks as she sobbed. "My breasts! My beautiful breasts!"
Hyperbunny was slumped to on the floor, leaning against her glowing blue bubble shield and covering her face with her hands.
"No, no, please, no! I don't want that to happen to my breasts! I love my breasts! It's not fair! Why is this happening to me?"
Dr. Electrode scanned Hyperbunny's chest. "There's still some time before you explode. I can try to surgically remove the the contaminated tissue before it converts too much of your breasts to explosive."
"You can?" Hyperbunny blinked back tears and sniffled.
"Understand that even if the surgery goes well, your breasts will never be the same. I'll do my best to save as much as I can, but they won't be large anymore. You can expect your breasts to be little bigger than mine."
Hyperbunny groaned and flopped onto her back, covering her face with her arms.
"Get Spacewarp to send me somewhere the explosion won't hurt anyone," said Hyperbunny, her voice shaking, her cheeks wet with tears, "I'd rather die."
"I'm afraid that's not an option," said Spacewarp as she appeared out of a ripple in the air inside Hyperbunny's shield.
The slender young woman wore a black and white suit with a swirl pattern across her medium-sized breasts. She put a hand on Hyperbunny's shoulder, and then they both vanished as quickly as Spacewarp had appeared.
Minutes later Hyperbunny was lying on an operating table in the medical center and Dr. Electrode's gloves were red with Hyperbunny's blood.
Hyperbunny's teeth were clenched and tears were running from her eyes. A scalpel slowly sliced chunks of breast away and then black-gloved fingers set the pale globs of fat on a tray beside the table.
"I'm sorry you had to be awake for this," said Dr. Electrode as she worked, "We had no time for general anesthetic. The pain must be terrible."
"It's not that," sobbed Hyperbunny, "The pain isn't so bad. I just... I can't believe I'm losing my breasts! Why couldn't I just die instead?"
"I'll do everything I can for you and Novahawk. There are options. Implants and prosthetics can be very effective. You won't have the best breasts on the team anymore, but you'll still be an amazing superhero, and that's worth living for."