Everyone remembers where they were the day all hell broke loose across the world. It's hard to forget a thing like a glowing, slime green planet showing up in the sky. It's hard to forget the day a man from another world declares war on Earth and it's heroes...

Buttercup and Butch had been going steady for a few months. Buttercup was happy, so happy, until the day he humiliated her in front of the entire school, by reading aloud long passages from her journal. And laughing like an escaped mental patient. She felt like she had shared a piece of herself with the Rowdyruff Boy that she had never shared with anyone else, and Butch had thrown it in her face.
She had never angrier with him, not even when he had been a bad guy. Then she had punched him in the nose, felt the cartilage crunch under her knuckles. Butch had fallen back, shocked, blood gushing from his nose.
"Consider this a break-up." Buttercup had said, forcing back tears. She would not give Butch the satisfaction of crying in front of him.
She had barely registered flying up and out of the school yard, but the next thing she knew, she was standing in Townsville Dump. Buttercup's keen vision picked up just the person she had wanted to see. She flung herself at him, nearly knocking him back with her considerable strength.
"What's the prob', green-eyes?" Ace had asked.
She had muttered a choked response into his jacket. Ace never seen Buttercup so upset about anything. Ever. And suddenly, he had the impulse to kiss her, but he wasn't stupid enough to think that was what she wanted right now. She'd probably have slapped him if he tried. Buttercup needed a friend right now, he concluded, and she had come to him of all people. "Don't screw this up, Copular." Ace had thought to himself.
He had settled for brushing a strand of her short black hair behind her ear, when he saw it's pale glow creeping across the sky like a fading bruise.
"Buttercup, look. Do ya see that?"

At the KND Treehouse in Sector V, it had been like any other day. Numbuh 3 and 4 had been fighting over the remote; Wally wanted to watch a monster truck rally while Kuki had insisted upon the Rainbow Monkey Movie. Numbuhs 1,2, and 5 had been eating candy from Numuah 5's special stash and talking strategy. Numbuh 5 had been about to tell Wally and Kuki that if they didn't both knock it off, she was going to unplug the TV set, when Numbuh 2's alarm system when berserk.
"Numbuh One, scanners are detecting- what the heck! That can't be right!" Hoagie had exclaimed.
"Spit it out, Numbuh Two." Numbuh One had said impatiently.
"You're not gonna believe this, Nige, but the scanners have detected an incoming hostile...planet!"
"Yeah, right, Hoagie. You're scanners must be on the blitz or something!" Wally had snorted, as he tried, unsuccessfully to pry the remote out of Numbuh 3's grasp.
"These scanner were built by me and the Dexter of DexLabs as a pet project. They've never been wrong before." Numbah Two said firmly.
"Well, in any case, we best get done there an' check it out. Part o' the sky's turnin' green. Numbuh Five doesn't like the looks o' that." Abigail said.
"Agreed. Numbuh Two, Numbuh Three, I need you to contact, Moonbase, Sector E, and any other Kids Next Door Headquarters you can think of. I need to know if they're seeing this. Four and Five, you're with me."

Ben Tennyson, long time defender of Earth, wielder of the Omnitrix, etcetera, etcetera, had been fighting the DNAliens with his cousin, Gwen, and his ex-rival turned best friend, Kevin Levin. He hadn't noticed anything was different until the hideous creatures began fleeing.
"Hey, get back here," Ben had said as the Omnitrix timed out. "I wasn't done pummeling you yet!"
"Uh, Ben, I don't think they're running from you. Do you see the same thing I'm seeing?" Gwen had said, tapping him on the shoulder.

Dexter had been dreaming up his latest invention when his scanners, the same he and Hoagie Gilligan had built together not long before, went off.
"Dexter, detecting hostile planet." Computress had informed the boy genius.
"A hostile planet? I shall have to debug you if you keep making up such crazy claims." Dexter had said in his thick Russian accent.
"I assure you, Dexter, it is not a computing error. Look onscreen."

All around the planet, reports were coming in about sightings of a strange, eerie green sphere in the sky. Photos of it showed up all over social media, the news, and even late night talk shows. No one knew quite what to make of it. DexLabs and the Kids Next Door had informed people that the strange planet was hostile, but nobody paid them any heed. They were just children, after all. The government was so insistent that the planet, identified as Planet Fuse, had to be non-hostile, that several important leaders and heads of state had agreed to meet with a few of its ambassadors.
It wasn't pretty.
Most were captured or killed, but a few were released, seemingly only to deliver Planet Fuse's message. That the planet's ruler, Lord Fuse, had no intention of making peace with Earth.
The world went into panic mode. It seemed like nowhere and nothing was safe. Civilians and heroes alike were being picked off the streets. If they returned alive, they were never quite the same. And on top of that, Lord Fuse sent his minions all over the earth.
Most were easy to defeat, and some people thought Earth might be close to its victory over Planet Fuse, until he sent out Fusion versions of Earth's greatest heroes. Green-skinned Powerpuffs destroyed Townsville. Fusion Ed caused chaos in the Cul De Sac. Ben Tennyson was reportedly seen wreaking havoc in his beloved home town of Bellwood. Hideous, red eyed versions of Billy and Mandy had nearly turned Endsville into a dump. No one knew had Fuse had obtained samples of the heroes' DNA to create his twisted Fusion versions, but everyone knew Earth was going to suffer a devastating loss unless someone brilliant devised a solution.
That's where DexLabs came in. Dexter McPherson, the CEO of DexLabs, put out a call to arms for all of the planet's heroes. At first, most of the usual crowd answered the call: Ben Tennyson, Samurai Jack, the Powerpuff Girls, the Kids Next Door, Rex Salazar, but eventually, even villains and ordinary children joined the fight.
But thing were chaotic in those early days and old rivalries reemerged, most notably when Mo Jojo famously knocked Buttercup into the sea during a heated battle with the Powerpuf girls. If Earth's heroes didn't ship up soon, Lord Fuse would win the war.