Gonna have some things that might be different from the anime/manga. Picture is of Nate.
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Nate flew along with his maneuver gear, checking for wall breaches and other things. The Titans were in fact here, but hadn't attacked this part of YouTubia yet. Wall Sly had been breached and a minority were evacuated, but Wall Sky and Wall Septic hadn't been touched.

Wall Sky was the one he was patrolling. It was the middle section, but where most of the training and fighting were done. For Nate, he was the fifth out of five to pick his corp, so he picked the Survey Corps. The recruits that were not in the five got either Garrison or Survey, not the Military Police. Mark and Jack had chosen Survey Corps, against Jack's fathers wishes. He wanted his son to become the king of YouTubia over in Wall Septic. The Fischbach family was the closest to them, with both father's knowing each other since they were kids.

Nate shook his head and kept going. Why did Mat have to pick Military Police? He could of joined Nate, with Brett, Morgan and the others. He sighed and landed on a roof.

BAM! BAM! BAM! ........CRASH!

A gust of wind flew by. The Titans had breached Wall Sky. Nate sighed, this would be his first Titan encounter. Where was everyone else? Why weren't they attacking?

Nate swallowed some air and jumped off the building, going after the Titans. He swept by the smaller ones pretty easy, as he was trying to get to the base.

<At The Base>
Nate opened the doors to the leader, Felix. "WALL SKY HAS BEEN BREACHED!"

Felix spun and said something to Wade, the messenger. Wade took off and Felix smiled. "We know Mr. Sharp." Nate nodded. "We are sending soldiers now, so get out there and save us." Felix shooed him out.

<In The City>
Nate jumped from roof to roof, trying to spot Brett and Morgan. He spotted Adam and Ross along the way, fighting some 3 and 4 meters. He saw lots of 6 and 7 meters along with their shorter cousins.

"NATEEEEEEE!" A male voice yelled. It was Brett, with a 10 meter holding him hostage in its vice-like grip.

Nate spun around and dove for the 7 meters, but was knocked away by an 8 meter. He hit hard brick on a roof and cut his legs and arms. His glasses shattered and fell, now lost.

"NATE HELP!" Brett was only a few feet away, so Nate catapulted himself foreword, but a 9 meter Titan was below him. It's jaws snapped upwards, tearing Nate's right leg off. Nate screamed in agony as blood flowed from the spot that held his leg.

Nate once again hit brick, but grabbed out and catapulted himself again to aid Brett. The 10 meter opened its mouth, steam pouring from its foul mouth.

He hopped faster and faster until he grabbed Brett's arm. He flung the younger male out of the beasts jaws and tried to get himself out. Brett reached for him, but the Titan closed its mouth, its teeth chomping off his left arm. Saliva covered him as he fell down the Titans throat and into the stomach.

"HELP!" Nate cried. He buried his face in his only hand. He was sitting in a giant pool of stomach acid and blood, which was not good for his nose. Nate had to try to not throw up.

"SOMEONE HELP ME PLEASE!" Nate yelled, louder than before. He wept silently as he knew he'd soon be dead, just a memory.

"I CAN'T LET ANYONE DIE! PLEASE HELP ME!" Nate yelled. Rage covered his vision.

'Why do I have to die! Will Brett even survive! I want to help!' Nate thought.

"I WANT TO HELP!"

<Outside>
Brett wheezed as the 10 meter came closer again. He was leaned against a chimney, breathing in and out. Nate just sacrificed himself for him! Why couldn't he help!

"RAHHHHHHHHHH!" Suddenly, the 10 meter Titan burst into a mess of blood and skin. Another Titan stood up on top of the dead one, roaring.

It was a 15 meter Male Titan with shirt kept raven hair and glowing red eyes. It resembled someone familiar to Brett.

The Titan roared again before taking off and attacking other Titans. It tore them apart and beat them to a bloody pulp.

The Titan turned, running and tackling a 16 meter. It tore the head off the other Titan, roaring in dominance.

<Later>
After a while of that Titan tearing apart others, it stopped and fell to the ground. Every Titan that had breached the wall was dead, but more were coming. They wouldn't arrive till later, which was good.

A person was moving around the Titan, lying on its back. It was male.

Brett landed next to the male and he looked up.

"N-Nate?"

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There you go!

Oh and here is Titan Nate!