This is my craziest idea ever, put into practice. It is kinda connected to my main One Piece story, but if you happen to read that story, you can see this as an alternate possible future, so don't think too much about it. There is a few spoilers tho. If you don't read that story, I don't think you really need to, on general, I think I explained enough on the chapter so that everyone can follow most things. And I already posted this story in other sites, and until now I didn't get someone complaining that it was hard to follow because they didn't read the One Piece one, so I think is safe.

Now, as you already saw, this is not simply a DxD x One Piece crossover, but a multi-crossover, so here are the series that will be on this story:

DxD, One Piece, Naruto, Bleach, Demon Slayer and Pokémon(yes, Pokémon)

Now, to what matters. I started DxD sometime ago, and I actually enjoy it. Yeah, it obviouslly has its flaws, but in general, I am having fun with it. And, if is not noticeable enough by the synopsis, I am fully on the side of the fandom that likes Issei and hates the ridiculous amount of oc centered fics, or crossover fics that kick Issei out. I sware, most crossover fics with DxD, the author despises DxD.

So, I am doing it. Personally, no crossover between DxD and Bleach does it for me, don't get me wrong, there are good written ones, but not one I can truly enjoy, and I hate all the crossovers with Naruto. Why people like sucking up to Naruto so much is a mystery for me. I blame it on nostalgia. Yes, I know, I am probably on the more unpopular side, but fuck it. Naruto is not getting paired with anyone on this fic(there will be no bashing), deal with it.

Originally, I was hesitating on pairing Issei with certain characters, but then I thought, if authors take it as free game to pair the girls that should be with Issei, with other characters, than is free game for me to pair whoever I want with Issei. I know what will be the response for this, and if you are curious or already want to curse me in the reviews, a part of the harem list will be on the notes on the end of the chapter.

This fic is made to be focused on DxD, except for One Piece and Pokémon, everything else will be adapted to fit the DxD world.

And, like I said, I am pretty aware of the type of response this fic will probably get, but, well, whatever.

Good chapter

The World Government fell.

Im was defeated after centuries being the Absolute King, surpassed by the one who broke the logic of the world, Monkey D. Luffy, the man with powers over darkness and multiple other powers. The man who reached territory never before imagined, the strongest man in the world, that had surpassed all that came before him.

The Straw Hats, despite all their accomplishments and importance in overthrowing the Old World Government, were still infamous and feared throughout the world. Which was ironic, considering the contributions of some of the crew members. Among them, as one who wasn't exactly a member, but someone who practically lived with them, Vegapunk.

After the government's failed attempt to assassinate him, a failure, of course, thanks to the crew's interference, he had joined them, but purely out of his interest in continuing his research. And just like the current Pirate King and several others in the crew, he had fulfilled his dream.

The form of energy that was once lost was again discovered, and thanks to the scientist, it was spreading across the world, changing society as a whole. Not only that, but Vegapunk reached his goal, his finish line, reaching the same scientific level as the most advanced civilization in the world, the one that perished eight centuries ago, had. But his greed was comparable to that of a pirate.

And now, Vegapunk wanted to go further.

The ancient Kingdom, the society of the Lost Century, their science and wisdom were indeed very advanced compared to even himself a few years ago. However, they were still far from omniscience or anything of the like. Even they had limited knowledge, in the end. What Vegapunk now had set his sights on, was what was beyond the knowledge of the Lost Century.

"Little time, very little time..."

However, he was already an old man. Inevitably, his time would come... or was it really inevitable? He thought of a lot of things, easy when you're the most brilliant mind in the world.

He considered letting his original body pass and continuing the research with clones, but discarded the idea. If he were to continue advancing knowledge, he would want to do it himself. Then he had a bolder idea.

Immortality. It wasn't a fantasy, at least not completely. Im, centuries ago, had acquired it. As long as the idea of immortality existed, people's will and desires would make this concept manifest, in one way or another, after all, that's how Devil Fruits worked. In the case of immortality itself, the Ope Ope no Mi was the key, the fruit that was in the hands of one of the members of the Straw Hats.

Of course, it wasn't so simple, and there was a sacrifice to be paid if the user of the fruit decided to make someone immortal. It would end with his death. Those were the basic rules, but following Luffy's example, Vegapunk decided to take other routes, break the rules established by this world.

Cloning Trafalgar Law's fruit was relatively easy, the scientist already had countless amounts of practice with these things. The challenging part came later. He didn't want all of the fruit's abilities, just the ability to perform the Immortality Operation, and without the downside. It was somewhat challenging, and at the same time enlightening, the whole process of recreating a fruit based only on a single ability of the original fruit.

But for him, it was just a matter of time. Finally, he had created a unique fruit with the power to conceive immortality and placed it in an object, a weapon that utilized the energy of the Lost Century, meaning that it had infinite energy. In this way, the negative side of using the immortality operation had been overcome, and in theory, he could use it as many times as he wanted.

Now, it would only take one shot, and immortality would be in his hands.

Vegapunk was currently in his lab on the Sunny, alone, ready to take that giant step that would allow him to discover so much more about the secrets of not just the world, but the universe.

"Ready... finally, it's ready..."

Vegapunk's eyes glittered as he watched the weapon in his hands, which were shaking as if he were in the middle of an earthquake.

A few moments before...

"Yo, Luffy, want to train a little?"

In the training room, highly resistant by the way, Zoro, the best swordsman in the world, asks his captain, the strongest man in the world. The two were tall and muscular, but their overall appearances had changed little since Im's defeat. Well, the one big exception being Luffy, who now constantly had white hair. But that wasn't a sign of lack of vitality, quite the contrary, the captain had plenty of it.

- Sure, it'll be fun!

Luffy responds with a big smile, to which the green haired man responds back with a defiant smile.

They disappeared and reappeared in front of each other with katanas in hand. Their blades met dozens of times in a few seconds. In terms of technique, Zoro seemed to have the upper hand, but in everything else that wasn't sword technique, it was clear that Luffy was superior.

They were just warming up, but both ended up getting a little too carried away and covered their attacks with the advanced form of conqueror's haki.

A shock wave passed through the Sunny, causing the entire ship to shake. Normally it wouldn't have done anything more than annoy the crew a bit, though today...

With the tremor caused by the attack, Vegapunk's trembling hands failed to continue holding the weapon, which fell to the ground. For the doctor, time seemed to begin to pass slowly as the gun rotated, until it hit the ground with the end of its barrel.

A single static spark shot from the weapon. For a second, everything looked normal. Then more arcs of static started to come out of it, and in the next instant, a wave of energy spread from the lab to the entire Sunny.

"I shouldn't have made this pistol in less than ten minutes..."

Vegapunk thought to himself, already imagining how the others would react.

That was the fateful day the Straw Hat Pirates accidentally became immortal.

...

"Other worlds?"

A few years had passed since the incident, but the Straw Hats hadn't changed a bit. Or rather, almost hadn't changed a bit.

At the moment, they were gathered on the deck, and Robin and Vivi were holding small children in their arms. Luffy's first children to be precise. They still had a few extra children, but most were not on deck and instead sleeping in their rooms.

Years ago, after accidentally becoming immortals, they didn't know how to react. Until Luffy thought that, at some point they were going to run out of adventures to go and this almost made him take Vegapunk's head. Fortunately, the doctor calmed the captain down, promising that he would find a way for them to still have a lot to do. And now, here they were.

Talking about the process of immortality, Vegapunk still had the weapon and could quite easily recreate more of it. Though, it was not necessary for the kids, as it turned out their lineage factor already carried the immortality from their parents, they would only age until their bodies reached their physical peaks.

"Another world? Like the space?"

Chopper asked confused, confusion that seemed to be shared by most.

"No, no. I am taking about even beyond space. Luffy, have you ever wondered which dimension you enter using your door powers? Or, for example, I heard that you guys once found an alternate version of yourself, am I right Captain?"

The user of the straw hat nodded. He couldn't help but chuckle a little at the memory.

"What's with these things, old man?"

Bonney questioned. She was the least patient with Vegapunk.

"Ahem, there are dimensions, universes, far beyond ours. Unknown worlds, mysteries and science that are beyond me, and beyond all of us."

Vegapunk's eyes shone like stars as he explained. Not just his, actually almost the entire crew had similar reactions. Luffy and Bonney for example looked forward to new adventures, Chopper, Usopp and Franky were as delighted with their discovery as Vegapunk was, Zoro wondered if this would give them the opportunity to get even stronger, and even Sanji thought about things such as, what kind of unique ingredients and cuisines he could discover. Without exception, everyone in the band was delighted with the new possibilities.

"And did you find a way to these worlds?"

Law asked, wanting to confirm once and for all.

Vegapunk's smile already served as an answer.

"Using the Doa Doa no Mi as a base, it became possible."

He spoke, followed by a moment of silence.

"AMAZING! LET'S GO TO THIS OTHER WORLD NOW! WHAT WILL THE MEAT BE LIKE THERE!"

Luffy squealed in excitement, already salivating purely with his imagination. Vegapunk's few words had already excited him as much as it was possible to do.

"If my dear said so, then hurry up Vegapunk. Open that portal at once"

Boa Hancock said, no, ordered the scientist. The only people she treated with affection, or respect, were still just Luffy and her sisters by marriage. Though that would soon extend to the children as well.

"Wait a minute! But what about our world, will we be able to get back to it?"

Vivi was the one who asked the question. She was as excited about the idea as the others, but the thought of never seeing Alabasta again in her life, or even being able to show her children the island and kingdom, made her sad.

Vegapunk of course, knew what the bluenette was thinking.

"Don't worry Vivi, I wouldn't want to leave our very interesting world, for nothing. I've already built an anchor that will keep signal across the worlds, allowing us to return here whenever we want. Of course, this depends on the navigators. What do you two say?"

Nami and Bepo answered the challenge with a smile.

"It doesn't matter if it's from island to island, or from world to world, the Straw Hats have the best navigators, so there's nothing to worry about."

The redhead replied proudly. Luffy smiled at his wife's attitude, and made an affectionate gesture, patting the top of her head.

"What she said."

Bepo added his part to the conversation as well.

"So..." Vegapunk pulled what looked like a TV controller out of his pocket. "Let's take a look at what's beyond."

He pressed a button, and in front of the Sunny, the air seemed to break apart, as what looked like a gigantic door glowing brightly formed.

The group's excitement was indescribable.

…

The multiverse. An infinity of possibilities and worlds.

Even though a lot of time had passed, the Straw Hats knew that they had explored only a tiny fraction, probably less than that, of the possibilities that the multiverse offered.

And even after countless experiences, certain things were just constant in life.

"Luffy, can you stay still?!"

Zoro said through clenched teeth, almost grabbing the captain and forcing him to sit down.

"No, I want to see him!"

And the brunette, or rather the white-haired one, said it almost like a child complaining.

At the moment they were not in their original world. They had stopped in a world that had similarities with several others they had passed through. Advanced technology, but not so much to the point of being particularly impressive, and a world dominated by the human species. Or at least that's what it looked like at first. They felt several obviously non-human presences, and already having previous experiences, they seemed that this world must have another society behind it, predominantly of magic, a characteristic shared by several other worlds. They also made friends with a particular group, but that was story for another day.

They were on the Sunny, using Vegapunk and Franky's technology to be virtually undetectable. The reason they ended up on that world was simple, Hancock was having a new child, and to avoid possible problems, they would avoid going to other worlds during the process.

"You can enter Luffy."

Chopper announced from the door of the infirmary, and the captain was already appearing inside.

There, Hancock was on the bed, Law was beside her, and both of them were looking at a small baby in her hands.

"Do you want to hold him?"

It wasn't exactly a question, since she already knew the answer and was already stretching her arms so that Luffy could hold the child.

"Shishishi. What's up, little guy?"

The captain speaks laughing, holding his son by his armpits, lifting him in the same direction of his face. The baby looks momentarily intrigued by his father's appearance, then bursts out laughing.

"What name do you want to give him?"

Law asks the two.

"Marianne-chan was looking at some names of that country she was doing those drawings in, and she said she has one that suits us perfectly." Luffy says, looking proudly at his son. With his powers over the soul, courtesy of the Soru Soru no Mi he took from Big Mom, he noticed something curious within his son's soul, but it was dormant and the captain felt it was harmless. It was still curious, but it was something that could wait. First, everyone should know the name chosen for the child. "Issei!"

o, here is a part of the harem list:

All canon girls, as of Shin DxD volume 2(yes, absolutely, the ones that appear on the dream included, I mean every canon)

Hinata

Kushina(widow)

Tatsuki

Rangiku

Nezuko

some OCS

Grayfia

Serafall

now, for other pairings:

Sirzechs/Tsunade(I could not take Grayfia out of him, and not let him be happy with someone else)

Saji/Momo/Ruruko

Ichigo/Orihime(I am still not sure if I will add Rukia, or if I will do Rukia/Renji)

Sona/Sairaorg(I know it is an unusual one, but a friend told me about he saw them together, and actually, they together make a whole lot of sense when you think about it)

and yeah, this fic is partially made because I greatly dislike how Naruto crossovers are here, so no pairings for Naruto(I am sure everyone is civillized, and no one will curse me on the reviews for this)

but I genuinelly believe, that, taking canon Issei and canon Naruto, they would actually become friends, Naruto would probably like Issei a lot, and vice-versa

This was just a introductory chapter. The idea, as crazy as it sounds, actually started making more and more sense, the more I looked onto it. Issei, meaning honesty, is a fitting name for any children Luffy could have, lol. How dragons are said to be in DxD and, a lot of other small details, that the more I noticed, the more this idea actually seemed feasible. The following chapters will be posted soon.

And if you absolutely hate this idea and think that pairing Issei with Hinata and Kushina(plus other Naruto girls that I did not put on the list), is some type of sin against humanity, feel free to rant on the reviews, lol. Won't change anything tho, but might make you less frustrated, I guess.