Mob psycho 100 X One Piece crossover
I don't own One Piece or Mob Psycho 100

Mob's day started normally before being sent through a suspicious portal, and he went to Reigen office as he always did. The older man had called him because of a reticent gost who appeared to be a pirate.

Once there, he learned that the man refused to pass away before finding something called the « One Piece », some legendary treasure every pirate was after. The strangest thing (but not as strange as some things he saw, like the whole psycho helmet cult and giant brocoli affair), was that he somehow came from another universe. Since he was fairly aggressive, Mob exorcised him with a wave of hand.

That's when it happened. The spirit, while being sucked out this existence plane turned his arms black and grabbed poor unsuspecting Mob, taking him into the vortex. They both disappeared before Reigen could move. He slowly fell on his knees, muttering a littany of no. He then passed out, like two dozen or so of people in the city . When he awoke, he had the weird feeling of forgetting something really important but couldn't remember no matter how much he tried. He would later dream of a small figure in black and a warm smile, and so did the others.

((ooooooooooooooooooooooooooooooooooo))

In the blackness of the space between universes, Mob was floating unconscious, protected by a bubble shield. As a living boy, he was separated with the spirit and sent down, on the world of lands and sea, pirates and marines, treasures and dreams. So he fell, down and down, like a falling star and still unconscious, before landing in a big crater. The sound and shock wave shaked the land of the insland and a cloud of dirt rised, signaling his position even you somehow managed to miss his arrival (wich was pretty hard).

During is sleep, one of the most feared pirate crew was debating about who'd go look. Finally, tired of the shout ang fights that were already starting, Whitebeard sent Marco since he could fly and would be faster. It didn't take very long, the island they stopped on was small and inhabited, in the middle of nowhere on grand line. So the Phoenix was really surprised when he found a little boy, apparently asleep, without a scratch despite the awfully violent landing. There wasn't even a spot of dirt on his black uniform. He looked young, maybe around 15, was small and had a bowl cut. It was the only characteristics you could list. His arrival looked like the work of Kuma's devil fruit but there wasn't the distinctive paw mark on the soil. Still, it was the most probable explanation so he'd have to ask.

He gently scooped the tiny and weightless body, who seemed devoid of any muscle in his claws and flew back, without waking the little boy. Once one the beach, he carefully lowered him in the extended hand of his father, before transforming back. He called for the nearest nurse, but apparently the stranger was just asleep. So, he slowly shook the soulder of his discovery, trying to appear nonthreatening but still on gard as enemy could be everywhere. Plus there was something strange with the boy's aura, but he didn't know what.

A pair of expressionless black eyes opened and he sat, still in the palm of the giant captain, before looking around slightly surprised. He then scrunshed up his nose as if trying to remember something before relaxing, looking a bit puzzled. Not the reaction one often has in such situation. The boy turned up his head to observe the owner of his current resting place and asked shyly.
« Hello sirs, could you please tell me where we are ? »
During his wake, the lieutenants had gathered around, and one answered :
« We are on an island in Grand Line. Now, what we'd like to know is who you are and how you ended here. »
« Uh my name is Kageyama Shigeo but some call me Mob, and I'm from... from... Strange, all I can remember is a big brocoli ... I'm pretty sure I had a family though, but my mind is full of holes... »
A lot of pirates wondered if his expressionless was because of amnesia or just natural. Surely, no one could be so calm ! Apart of Marco of course but he was usually an exception in this domain.
Marco asked their father :
« What should we do yoi ? I can tell he is not lying but enven taking him to the nearest island can be dangerous. Can you fight Mob ? You don't have an ounce of muscles yoi. », turning toward the child, a sceptical look on his face.
« Oh, I think I can defend myself, but I don't like hurting others. »
« Joy, we got a pacifist, really useful. Let's see what you've got! »
And with that, one of the lower ranking man took a saber out before advancing toward Mob who had been lowered to the ground during the conversation.

« Should we let him yoi ? The kid could be severely harmed if he is too weak, » asked the 1rst division commandant. But his captain only laughed before pating him on the back.
« Don't worry son, my instincts tell me there is more of this kid that his apparence suggest. In fact he will probably win. Look more closely with your observation haki. »
He was right of course. There in the middle of the circle formed by his curious comrades, a strange energy surrounded tighly the boy. It was not haki tough and soon as it concentred it was visible with bare eyes. Ignoring the multicolred aura, the fighter from his crew rushed forward and slashed his weapon toward the unmoving kid. There was a loud SHTONG as the lame bounced on a barely visible barrier and broke. The man stared dumfounded at the boy, but before he could land a hit, Mob moved his hand, power encasing it and sent his opponent in the air violently. He landed far away with a loud crash and the rest of the crew stared, before laughing.
« Did you see how he flew ? Be careful Marco, he's going to steal your place of best flyer ! »

« But seriously kid, how did you do this ? You ate a Devil fruit ? And could you do more ? » another asked, exited.
« I don't know what a Devil fruit is, and I was born with psychotic powers. I'm at 34%, but I didn't use a lot of force... Is he okay ? »
Mob looked at the captain, concerned.
« Gurarara ! Of course he is ! We are pirates after all ! But I wonder, what do you mean by 34% ? How do that work, and what will happen at 100 % You'll collapse ? »
« No, it's my explosion point. »
« Oh shit, an human bomb ! »
Suddenly there was a lot more place around him. He seemed confused.
« I don't mean it literally you know, but maybe it better if you're not too near when it comes. »

((ooooooooooooooooooooooooooo))

Later that night, everyone was eating on the beach, roasted meat and exotics fruits while the alcohol flooded. Mob was seating around a campfire next to Marco and Whitebeard. He was lost in thoughts and jumped when an enormous hand landed on his shoulder, before looking up.
« Yes ? »
« Tell me Mob, would you like to be part of my family, my son, and sail on the sea with us ? We'd teach you what you need to know and if this life is not for you, we'll leave you on a safe island. »
« You're sure pops ? » Marco wasn't really surprised, with the power the kid displayed, and his missing memory.
« I am. »
At that, Mob beamed a beautiful smile, eyes glistening and nodded, a little blush on his cheeks. And the men around told themselves that they will do their best to make him smile more and break his expressionless mask. Really, who'd thought someone seemely so plain could be this cute ?