With a soft gulp, The Charmander with a Red cap watched away as The fight was to go forth. His eyes darted around, Keeping a good eye on His Charizard partner who kept a close tail on the legendary in front of Him. 

The Legendary's name Was Mewtwo, And currently He wad Training with The Charmander's Charizard; Zaal

The Charmander Was named Red, One of the many  former Humans that were turned Pokemon; A HuMon.

Before their eyes, The Mewtwo would turn around suddenly and unleash their classic move; Swift. Red could theorize it was moreso to not Hit Zar, But to make get him off Of His trail, So The Charmander would decide to quickly Hit back. "Zaal, Fight back with swift too!"

And Zaal would follow, Him unleashing His own set of stars and colliding with the Mewtwo's in a cloud of explosion between the two...

"Use Mega Punch...Please!" Red all but whispered,  Hands together and Closed eyes. It was now or never, The Mewtwo was off His game now, It was now or never, He just hoped His charizard heard his plea...

And it seemed like He did, Once He heard a gasp, Not sounding like His charizard.

"Ah...!"

Before His eyes, Zaal would smash his fist into the Mewtwos stomach hard. In reaction The Mewtwo let out a gasp of pain and the corresponding Blow flung Him Back the wall of the room. 

In seconds, The Charmander was from shocked to Happy. Gripping the edge of His Red cap happily as He ran forth with a smile. Zaal could See Him coming close and Sprouted a grin. "I see Your Happy." His voice was deep and Chill, Something like that of a usual Charizard.

"You did amazing out there!" After enough running, Red didnt hesitate to jump at his pokemon partner. "You've truly gotten Stronger Zaal."

Zaal smirked at the Praise. "Well, I did have a Good Coach to Train Me..."

"True, You two have improved since last time..."

Hearing that, Almost Simoutaneously. The two would look left, Where the voice came from.

From the wall where mewtwo got hit too.

He came out with a...Smile?  panting with arm over his injury.

"Impressive indeed."

[...]

"It's seems Your getting better Nowadays, Huh HuMon?"

Hearing His voice telepathically, Red swallowed the sandwich He chomped down on and turned to Red, His tail swaying with bread crumbs all over his face. "Yeah, This time I didnt even Need the Mega stone to bring you down a peg.  We truly are getting better, Right Zaal?"

The charizard Near just simply Huffed proudly before  going back to eating, His actions easily meant He agreed.

"Oh Yeah!" Red The Charmander reached into His pockets and pulled out...Some sorta silver Key. It was one with a legendary pokemon Symbol on it. "Thanks for this Mewtwo!"

Mewtwo knew what the Key was, A Token for beating Him back then. He smiled faintly, "It is No big deal, Just don't go Using it all the time. I won't be here all the time."

Red scratched His head, with a smile. "Ah, Don't worry about it! Even though  its fun battling with You, I wont abuse It. Honest."

Mewtwo was glad to hear that. He could Trust This HuMon well. "Good to hear."

For Backstory purposes, It all started long back; With their being rumors of a special labyrinth doors that could contain a Legendary Pokemon, One of the strongest pokemon, It definitely drove Coaches and their Partners to go and look. One of them was obviously Red.

And after Days of looking, He'd finally found one! Was it by chance? A Mere Coincidence? He wasn't sure but He was okay with either honestly.

And with His Team by His side, He was ever so ready!

It was a long hard battle fighting through for them, and It only got worse with Meeting Mewtwo, A strong psychic type.

The Battle with that...was Harsh to say the least. To Red, Mewtwo had proven why Legendary's were strong with wiping out most of His team. He even almost wiped out Charizard! But With the Help of a Megastone, It got them to pull through and bend up defeating Mewtwo!

In the aftermath of Healing them Up, Even Mewtwo. With Talks. Red got to see  Mewtwo in a good way, Rather than some legendary, He was also somewhat of aChilled Smart friend too. in the end, The fight sorta helped the two grow q bond, to which mewtwo would give them a Key, A Key that gave them access to this private dungeon at will.

And Here we are now.

"So, HuMon-"

"You know," Red intervened, "You CAN call me Red Y'know."

"Hmph...Red," Mewtwo corrected, "What else...Do You want to do? Im sure Training with Me wasnt the only thing You wanted to do?"

"True..." Red Nodded, Tail wagging from side to side, "I have one question..."

[...]

And it was an Hour later, That Red the Charmander, Would be balls deep in the legendary pokemon; Mewtwo, Slamming His cock in and out of the Legendary pokemon and having his ample backside clap and Jiggle.

"O-Oh My goodness, M-Mewtwooo~!" Red moaned.

"Ahh..~! Fufu~... Good boy~..."

He let out a soft chuckle as The Charmander continued pounding into him, making his large ass cheeks jiggle every time he slammed himself inside him.

Far away was Zaal was jerking off to the site in front of Him, Praising Red to go faster. "Go Faster Red, I Know You can do it!"

Mewtwo couldn't help but let out a soft moan as the Charmander inside him continued to pound away, his pace only increasing with each thrust.

Mewtwo would then out a soft groan as The HuMon Charmander continued to pound away at him, making his large ass cheeks sway every time he slammed inside him,  Mewtwo's his cock twitch as he felt the Charmander's cock pumping inside him.

Mewtwo would jerk himself off as He was fucked. "Ah...Mm~"

As if sensing something, The Charmander sped up even more, ramming his cock into Mewtwo like there was no tomorrow, causing both their bodies to bounce around wildly.

"Mewtwo...Y-Your soo tight...F-Fuck~" He groaned.

Mewtwo let out a low growl as The Charmander kept going, his hands clawing at the floor as his body began to sweat from how fast he was being rammed by The Charmander.

Mewtwo was always a stoic silent type...Until He got fucked really. There, He was puty in the hands of whoever fucking him~

"Ngh..." He grunted quietly as The Charmander pounded away at him, feeling himself get close to climaxing, Sensationa rising.

He smirked mischievously as he huffed and panted. "I think I'm gonna cum soon." he said softly, letting out a loud moan as his body tensed up.

Red gripped onto His ass tightly "M-Me too!!" He strained.

A smile formed on his lips as he heard Red say those words, knowing exactly what he wanted next. "Cum inside me then." he whispered huskily, looking back at The Charmander who nodded eagerly before continuing to slam his dick deep inside Mewtwo once more. "Ahh!"

and Red could hear a voice in His head...feeling like more of a command really;

cum inside me!

...But He didn't mind that~

Red looked back at His charizard partner before giving the final thrusts.

Zaal The charizard was orgasming, Cum spraying and Him huffing with a please expression at the sexy sight he saw~ "A-AaaaAAAAAAH♡"

The Charmander moaned happily as he shot his load inside Mewtwo, making sure that he filled him completely.

Mewtwo felt The Charmander's cum hit him deep inside, causing the already powerful orgasm to intensify tenfold. He growled loudly as he came, his body shaking violently. "A-Aaahh!"

The Charmander pulled out after finishing his load, leaving Mewtwo's hole gaping open and filled with hot sticky white goop. "F-Fuckkk...~"

Truly, Mewtwo was good at both training and sex~