One piece: The Brawler of the King.

A little break, tell us how Rex met Guana and Akula

On the going merry, men's quarters. Rex was sleeping in his hammock when he wakes up. He gets up and looks around, he sees he's not on arena island.

Rex: is actually happening 

Rex gets up and gets dressed. He walks upstairs and opens the hatch, he sees the straw hats just relaxing, then he sees akula and guana.( forgot to mention akula height. She talk that fire fist is right under her breast). He then see luffy and smiles.

Rex yeah it is.

Rex got up and enjoy they day.

Rex had fun with the straw hats, they ate, they fought. He got to know them and theirs adventures.

Timeskip brought to you by Zoro's bounty.

The crew was reading when Usopp brought up a question.

Usopp: hey Rex, I got to ask, how did you exactly get to arena island

Nami:yeah, and how did you meet akula

Chopper: and guana for that matter

Rex: you really want to know

Luffy: yeah it sounds fun.

Rex: alright. Here's how it starts. I once I set sail I did what any pirate did, tested my metal, so I took out they highest bounties I could fine, got in a way of a few marines. Soon got my bounty, they Leatherback Rex. So far no one could beat me. Then one day out on the seas I found myself on a island, it held so many great items. But then I stumble at an auction place. Where I met this little guy

He rubs guana head as he resumed his story 

Flashback

Rex walks through the auction place and finds so many things, weapons from giants, huge hordes of treasure, and animals from around the seas. He stumbles onto one cage far away from the others, inside it were chains as propane starred in aw, then the man running the place presented the creature.

Man: ladies and gentlemen, and pirates, may I present to you, the robotic, lizard

He removes the tarp as they see a small machine like lizard, covered in chain and brusies, just glaring.

Man: this creature is from the grand line and his body is coated with metal, non of our bullets, swords, or even canons can hurt this creature. And yii oh I think that's amazing he can increase his size. Now who wants to bid.

But unfortunately the people didn't want to bid for a disturbing monster and walked away. Rex watched as the creature distant itself from the others. Later that night while everyone everyone was sleeping. The chains of the lizard were broken. It wakes up and see Rex. He opens his cage as the lizard runs out. Rex smiles and sneaks off. Later rex was having a midnight snack.As he eats he notice someone watching him. He looks up to see the lizard hanging form the rocks. It claws down and moves closer.Rex goes and pets it but it back up. Then he gives him some foood as he eats it

Rex: your not bad, your just misunderstood 

The lizard looks attack him as he smiles. They continued to bond and to where the lizard started to trust him. They eventually went to sleep. When they got up the lizard decided to follow Rex to his boat. But then that man and his goons stop them

Man: hey that my creature, pay up or leave him

Rex: how about I do none of those things. 

The man smirks and snaps his fingers. His goons shot Rex in the back. But the bullets fell to the ground, dented. They try and use they swords but they broke. Then Rex turn around whilst growing large. He was now in his human beast form as he roars and punches the two goons. As he beast them up the man pulls out a rocket launcher and aims it at Rex.