A couple of months prior

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*Percy POV*

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Not long had passed since the reconstruction of Olympus was finished after the giant war and it was just another standard day at Camp Half-Blood, I was training when Annabeth came running up to me.

"Percy there's a meeting in the big house," said Annabeth.
"What about"
''Don't know, Chiron just said it's urgent and important"
"Let's go then"

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At the meeting

"Olympus has called an emergency meeting and they want the seven to go meet them." Said Chiron
"Why.. what for"
"They didn't say, but whatever it is it must be very important, all the major gods are attending' said Chiron
"Well we'd better go then' said Jason

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On Olympus

"Welcome to the heroes of Olympus" boomed Zeus as the seven entered the council room, "Let us get right to the point, Athena."
"Right, so when the universe came into existence, 6 stones were created which held the essences of the universe. They became known as the infinity stones, they are the space, power, reality, soul, mind, and time stones. They each hold power well beyond that of a god, and when used together omnipotence would no longer be impossible."
"What does this have to do with us' I complained, already getting fidgety and bored.
"Just listen! A short while ago we detected a huge power surge across the universe that can only be attributed to one or more of the infinity stones. We believe that someone is trying to collect all of them."
"What happens then?' asked Jason
Hades then chimed in "Potential death and destruction on an unheard of scale"
"Anyway" Athena continued "we sent Hermes to investigate and we found many dead and what remains of the tesseract, which we all heard about after the alien invasion of New York back in 2012. We had long suspected it contained the space stone due to its ability to open portals, and now we have confirmation."
"So what do you want us to do' Annabeth asked.
"We want you to be careful and to try and find the infinity stones, we believe that the mind and time stones are currently on Earth, unfortunately, we know the mind stone is with the Avengers, we know not however where the time stone is."
"Also be careful" said Poseidon.

*Line Break*

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Fast forward to the present

3rd Person POV

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In Wakanda

Through a portal, Thanos arrives on Earth to claim the last infinity stone, the demigods, trapped on Earth and unable to harm mortals had ultimately failed to retrieve any of the infinity stones. Percy was also dubious about bringing such powerful artifacts to the gods, who had shown themselves easily threatened and often worried about their own power.
As Wanda worked on destroying the mind stone and holding back Thanos, the Olympians and demigods were having another emergency meeting.

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On Olympus

"It is too late, the being known as Thanos has gathered 5 of 6 infinity stones as is on the cusp of getting the sixth." Stated Zeus
"What can we do" asked Percy hopefully
"Nothing, I'm afraid," said Poseidon crestfallen, "Because Thanos, though he is called the mad Titan, is mortal and the ancient laws prevent us from interfering, also this lies outside the realm of gods and inside the realm of mortals. You demigods are strong because you can occupy both realms, however, in this case, we can only try to save you by making you immortal."
"Then make all the demigods immortal," Percy said=
"Alas, we cannot' stated Zeus, 'The fates will not allow us to do so, however, we can make you seven immortal."
"No" the seven said in unison
"I refuse to believe all hope is lost" Piper said
"Yea! There must be something we can do!" Said Jason
"Send us to where this Thanos is, we will fight him" Percy said

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Meanwhile back in Wakanda

As Thanos says to Thor, "you should have gone for the head", he snapped his fingers.

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Back on Olympus

Percy POV

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All the Olympians suddenly felt a huge power surge. Then Hades said "It has been done, he has completed his task, death on an unprecedented scale."
"What do you mean"I Asked, when suddenly I heard Athena cry out and turned around to see Annabeth turning to dust. "No no no, you can't leave me, no no no!"
Then Leo started to turn into dust, then Jason followed by Hazel." What's happening!" Cried Piper.
Hades then said, "The death of half of all living things in the universe."
"BRING THEM BACK THEN!" I Shouted, "You are the lord of death are you not."
"Sadly I cannot, their souls will not go to the underworld, but to the soul dimension within the soul stone." Hades said sombrely. Then there was silence for a while while the demigods contemplated their situation. When suddenly, a clatter was heard…..

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End of Chapter One

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JK

When suddenly, a clatter was heard and I lifted my head to see Ares' spear hit the ground and watched as even Ares slowly disappeared.
"We shouldn't be affected, this isn't right at all," said Zeus
The clatter of Ares' spear was then followed by another clatter as Athena's spear also hit the ground, and then another clatter quickly followed as Poseidon's trident also hit the ground.
"No, not you too, don't go Dad, I can't lose you too!" I cried.
"The power of immortals has been overruled," Apollo said as he slowly disintegrated, "We will not reform from this, it attacks our very essence and existence."
Then Hades said, 'It is the end of the age of gods. Tell Nico …." He did not finish his sentence as he vanished.

When all was said and done, half of all life in the universe including immortals and those of myth and legend were annihilated by one snap by the mad titan Thanos. Thanos, content, went to his farm and rested on a 'grateful' universe.

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Actual End of Chapter One