Itachi stood on the deck of the Moby Dick, looking down at his right hand. After the chance encounter with Marco and his crew, he had decided to join the Whitebeard Pirates. In lieu of a tattoo, though, he opted to replace his old Akatsuki ring with one that bore Whitebeard's Jolly Roger. He had also updated his wardrobe to fit in better as a pirate. He kept his old mesh top, as well as his Konoha headband, but now he wore a black linen shirt over it, whose sleeves extended just past his elbows, a dark red sash around his waist, slightly baggy black pants with his weapon pouches tied around the thighs, and a simple pair of black sandals.
It had been nearly a year now since he joined the crew and had proven himself an incredible asset in many encounters, so much so that he was promoted to 4th Division Commander. Unfortunately, being a Commander came with a level of notoriety he didn't exactly covet. Being wanted by most major governments was a familiar feeling to him, but at least this time he was a wanted man as a result of choices he made of his own free will, rather than a result of orders he had been given. Still, his Wanted poster setting his bounty at six hundred and sixty six million berries was a less than welcome sight.
Itachi's attention was called to a scene playing out before him. Ace had just failed his 45th attempt on Whitebeard's life, and was being unceremoniously tossed by the old Captain from his quarters and onto the deck, causing everyone who witnessed it to laugh, except Itachi. It may not have been his place since he wasn't over Ace's Division or anything, but he approached anyways.
"You know," he said, offering a hand to help Ace up. "You would think that after the first couple of failed attempts, you would have learned you can't beat Pops. Why do you keep trying to kill the man who took you in?"
"Shut up!" barked Ace, slapping Itachi's hand away. "You don't know a damn thing about me so just mind your own business! I have no interest in talking about it, especially not to you!"
"Very well, then." replied Itachi plainly. "I'll be below deck if you change your mind." And with that, he turned around and went on his way.
Itachi was lying in his hammock reading a book on Devil Fruits he had borrowed from a crewmate when he heard a knock at his door. "Come in." he said. Ace opened the door, and Itachi set his book down. "Ace, what's on your mind?" Itachi asked, noticing the pensive look on his face.
"The guys forced me to come down here and apologize for blowing up at you. So I'm sorry, okay?"
Itachi simply smiled. "Apology accepted. No hard feelings."
This only served to set Ace off all over again. "Don't just let it go like that! You sound just like the old man! Always letting me off easy even though I don't deserve it!"
Itachi was surprised at that remark. Was he finally getting somewhere? "You feel like you don't deserve forgiveness? Why is that?"
"Because that bastard's blood runs through my veins! Gold Roger! I'm the son of Whitebeard's greatest rival and I constantly try to kill him but the stupid old man keeps letting it slide and I don't understand why?! He's supposed to be the great, invincible Whitebeard, the strongest man in the world, who shows no mercy to his enemies, yet he keeps letting me off the hook. If he's supposed to be this almighty pirate, this Yonko, then why does he do that?"
Itachi got up and moved to the door. He figured this would be a long talk. "Because Pops doesn't view you as his enemy, Ace. You may be Roger's son, but you're not the man himself, and Pops knows that. He doesn't see you as Roger's son, but as your own man, and he wants you to see yourself that way as well. Stay here, I'm going to go make some tea, and when I get back, we'll talk."
When Itachi got back with the tea, they continued their conversation. Ace revealed how since he was the son of Roger, he was hated by the world, and decided to hate it right back. Itachi also told Ace about his home and the things he'd had to do before arriving in this world. They talked about their family, with Ace mentioning Luffy and Itachi talking about Sasuke. By the time the conversation ended, they came away with a better understanding of one another and Ace in particular held a new respect for both Itachi and Whitebeard. Hopefully now the assassination attempts would stop.
After Ace left for his own cabin, Itachi made his way to the kitchen to drop off the tea kettle and cups he had borrowed, still reading his book as he went. One passage in particular caught his eye, as the page was worn, even more so than the other pages. It concerned the Yami Yami no Mi; its physical description, its powers, and its last known location, the latter of which was very likely outdated given how old the book was. He was nearly done with it, so he would have to return it to Teach soon.
Several months passed. Not many major things happened, aside from Ace being promoted to 2nd Division Commander. Encounters with the Navy were quickly resolved, the crew got along well, and times were good. He even was taught about Haki by an underling named Thatch, though he didn't get very far beyond the basics. Eventually, Itachi grew a little restless wondering about his current situation. Who or what brought him here instead of letting him die, and for what purpose? He needed answers, and he decided that he was unlikely to get them while serving under Whitebeard. So, one morning, he approached the old Yonko with a decision.
"I'm sorry, Pops. I have to leave and sail on my own for a while. I appreciate everything you've done for me, but I have questions that need answering, and aside from that, I need to carve my own path forward. You taking me in has allowed me to learn about how big and strange this world is, and I'm thankful for being allowed to be part of this family."
Whitebeard sighed, obviously sad at the idea of one of his children leaving. "I thought this day might come; I was just hoping it would be later rather than sooner. Very well, Itachi, although I'm sad to see one of my children go, I won't hold you back. Just remember that if you ever decide to come back, you'll always be welcome. You'll always have a place in this family. Now I need to figure out who will take your place as 4th Division Commander."
"If I may make a suggestion," replied Itachi. "I think Thatch would be a good fit. He's taught me much about this world, and about Haki in particular, and he's very well-respected among the entire division, as well as the rest of the crew in general."
"I'll take that under advisement," said Whitebeard. "Now, I know you're not one for a big spectacle, so it'll just be me and the other Commanders seeing you off. I'll have Marco prepare a boat for you and you can cast away this evening."
Itachi's farewell was a small affair, just as Whitebeard had promised. The other Commanders had tears in their eyes as they waved off their comrade and wished him well while he sailed out into the horizon.