If the timeline seems a bit off in regards to Thatch still being here, I apologize in advance. It works for this.
"Ace! Pops is looking for you! He's got a job for you and Marco!" Thatch called. Ace paused for a moment before redirecting his feet towards the Captains chair instead of his room where he had been going to write another letter home that he would never send. The Second Division Commander of the Whitebeard Pirates was curious, although thoughts of a rubber-brained idiot kept floating through his head.
'Hmm, I wonder if he found anyone crazy enough to sail with him yet... No, focus. Pops looking for me, focus.' He thought. When he got to the chair, he was unsurprised to find Marco already there, he rarely left Pops side, usually only to go chase Thatch for something, or to do paperwork.
"You were looking for me Pops?" He asked curiously.
"Yes, I just got a call from Jimbei, turns out Arlong's been causing trouble in the East Blue, trouble that he has just heard about." Whitebeard explained.
Now I'm really confused. I remember Jimbei talking about some of his men who left the ship and set off on their own about eight years ago, but nothing's been heard of them since. If those fishmen have really been in the East Blue all this time, then why hasn't any word of that reached here? Vaguely, I remembered hearing about some guy named Arlong back when I first set out, I think it was my first-mate that mentioned it...
"What kind of trouble?" I asked.
"The setting up his own Empire in the weakest sea kind of trouble. Considering his hatred of humans..." Marco said
Ace paled. If Arlong had gone anywhere near Dawn Island in the three years he had been away... the moment they found and threatened Dadan or Luffy... three years wouldn't have been long enough for a weakling like Luffy to get strong enough to take down a fishman, would it?
"Wait, why are you telling me this? Its not-"
"Nothing's wrong with Dawn Island that we've heard of." Marco interrupted. "Jimbei wants us to do him a favor and go take care of Arlong for him. We're to go to Conomi Island, find Arlong, destroy his Empire, and drag him back to Jimbei so he can deal with him on Fishman Island." He explained.
Ace nodded in understanding, but he was also confused. "Why send us, why can't Jimbei go do it himself?"
Whitebeard smiled. "It might be the fact that of everyone on this ship, my Second Division Commander, who also happens to be good friends with Jimbei, is the only one to have come from the East Blue. You know those Islands, you know how the people in that sea will react to Devil Fruits, and you know that sea. That, and you have family there..."
Nothing more needed to be said. Jimbei was giving him the perfect excuse to return to the East Blue without the government freaking out about two Whitebeard division commanders going to the weakest sea. Maybe while they were there he could 'bump into' Luffy... Whitebeard and Marco grinned, they could probably tell from his facial expressions what was going through his head right now.
"You leave in an hour." Whitebeard instructed. "Take your time coming home."
Ace just grinned. "Yes sir."
Oh, this was going to be a fun trip, he only hoped they'd be able to track Luffy down, and that Arlong did in fact stay far away from Dawn Island.
Dimly, he made a mental note to take Jimbei out to dinner next time he saw him.