Just as Coop and his new gang were planning how to stop Kat from taking over the Earth, Kat struck back.
While Coop and Dennis were searching for the frisbee in the bushes, Kat managed to wipe out Millie, Harvey and Lorne's memories of his evil with a smile on his face.
The two boys were shocked – all the things that happened at the Kat Nebula, all the troubles they went through, all of it was for nothing now. It was square one all over again.
"Kat? What did you do to their memories?", Coop exclaimed, as he saw Kat marveling at what he had just done.
He tried to fight Kat, risking being zapped by the eraser as well, but, thanks to his quick thinking and the frisbee, it didn't end like that fortunately.
Coop wasn't ready to face this defeat. Not after all he had been through.
As they were fighting, Fiona suddenly appeared at the worst possible time, running towards them. She wanted to see Coop earlier.
"Don't worry, Coop! I will…"
But the ray didn't allow her to finish her sentence. Coop pressed one of Kat's limbs against the ground, causing the gun to zap her.
Fiona's memories were erased forever.
Coop smashed the gun with his foot, but it was too late. He just lost Fiona.
"Oh! What are you doing to that poor little cat?", she asked him.
Dennis, who was watching all this chaos unfold, out of desperation said:
"Here we go again…"
Coop and Kat were still fighting. He couldn't accept what happened just now. He wanted Kat to pay.
But what was the point? After all, the memories were erased, and the gun was destroyed. Kat's not going to fix this and he's the only one on this planet who can build such devices as a memory eraser.
All was lost, but Coop fought anyway.
Fiona couldn't stand that innocent cat being hurt anymore and got between them. She picked up Kat in her hands, while Coop was laying there on the ground, dumbfounded.
"Coop, what's wrong with you? What did this little kitty ever do to you?", she proceeded to stroke Kat's head as he was making cute eyes at her, "Aw. You are so cute, aren't you?"
"He's an alien!", Coop shouted, "Try to remember!"
"Remember what exactly?"
Coop wanted to convince her, but Dennis shook his head. There was no point in talking to her about this now.
Fiona was rubbing Kat's stomach. Coop was disgusted by what he was seeing. He couldn't imagine this image in his head one minute ago even if he tried.
"Mr. Cat! Come here! Time to eat your fishy frisky bits!", Millie called from a far.
Fiona dropped Kat carefully on the ground, so that he could walk towards Millie. As he was walking, Kat victoriously smirked at Coop and turned away towards his owner.
Fiona waved goodbye to the cat and lent her hand to Coop to help him get up.
"Are you crazy? Why are you attacking animals? ", she asked him.
Coop didn't want to explain anything or hang out with anybody at that moment.
"You know what? We should all go home," he said angrily," Me and Dennis will talk to you about this another time."
"Whatever you say," Fiona accepted, "I hope you come to your senses by then.
As they were leaving the playground, Coop, out of frustration, threw the frisbee onto the little brick wall that Kat hid behind and left it there.
His biggest victory was taken away from him.
While Fiona was looking at Coop like he was crazy, Dennis was worried.
What were they going to do now?
After the memory eraser situation, Coop's life changed for the worse the way Kat intended it.
The two boys didn't find a way to bring everyone's memories back. Kat destroyed all his memory erasers, memory-related inventions and time machines that were in his scratching post before he went to the playground that day. He didn't want anything to be stolen.
Coop and Dennis still fought Kat the days, months and years after that huge loss, trying and succeeding in spoiling his plans. After every win they had, they were always blamed for all the damages. Coop, having accepted long ago that his deeds will forever remain unrecognized, accepted the repercussions thrown by his dad and, in rare cases, the police. Still, he tried to convince everyone that he wasn't crazy – that his sister's purple reject was an alien that would invade everyone if nobody did anything about it.
But, like always, nobody believed him.
Coop and Dennis desperately tried many times to explain the situation to her due to Coop's insistence that she will eventually understand, but Fiona just didn't believe anything that she was hearing.
Kat made sure he wasn't as careless as he was before. Their words were the only thing they had as proof.
"A planet full of alien cats? Time machines? A female cat that speaks with a Russian accent? Are you guys wackos? How do you come up with this stuff?", Fiona asked them in return.
Coop and Fiona's love soured not long after her memories of Kat's evil deeds were erased. The two were in different worlds.
Every time they hung out, Coop just wouldn't let it go. He always started talking about that evil cat Millie owned and how it was going to invade the entire planet forever. Although Fiona still cared about him, she grew tired of his constant childish ramblings and started to reluctantly distance herself.
She stopped visiting Coop that often, sometimes coming for an hour at most. Even then he still tried to explain everything to her, but all that did was further creeping her out.
On one of these occasions, Fiona even shouted at him, going home right after with tears in her eyes.
"Is this all you can talk about!? What's wrong with you!?"
Coop just wanted to convince her that he wasn't a freak. That all these crazy tales actually happened. And that she was there with him.
He wanted her by his side.
But eventually, Fiona stopped going outside altogether with anybody. Months went by and she was never heard from since.
Her disappearance really hurt Coop.
He started blaming himself for all of this. If he didn't fight with Kat that day, then she would still be here, helping him and Dennis. If he didn't go after that dumb frisbee, things could have been different.
If he didn't press Kat's limb…
If he just didn't press that stupid limb…
The what ifs didn't leave him for a long while afterward. He had lots of sleepless nights. He cried a lot over it.
And despite that, Coop still fought Kat, preventing him from taking over Earth.
It was his duty after all. It was the only thing left.