This is another short story.

It is also 100% canon, but I couldn't find a good place to put it again.

So look at this more like another filler episode. Not necessary if you're here for the main plot, but still an enjoyable read. (At least hopefully.)

Canonically takes place in the week between Ryo joining the LoV and Kai's appearance in chapter 4.
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CRASH!

     A baseball smashed through Ryo's perfectly clean living room window, landing a critical hit right into Tomura's face!

     "S###!" The villain clutched his nose, blood beginning to leak from it. "What idiot threw this?!" Grabbing the ball that had bounced off of him onto the floor, Tomura immediately disintegrated it out of spite, watching the flakes of ash drain from his hand. Spinner, Toga, and Twice, who had been lounging around on the couches with their leader, were a little startled as well by the direct assault.

     "What happened in there??!" Magne called from the kitchen, where she was preparing grilled ham and cheese sandwiches for everyone.

     "Just some stupid ball... Nothing to worry about. ... Ugh.." Tomura stood up, still holding his nose with one hand, to go take care of this mess in the bathroom.

     As he left, Ryo's footsteps came racing down the stairs. "Please don't tell me it was that brat!"

     "What brat?" Spinner inquired. "The one who threw the ball?"

     "Ughhughhh, yes! That brat! Stupid kid's going to-- Mmhhhgghhhh..." Ryo melted against the stair's railings, everyone staring up at him suspiciously.

     "Wait, has this happened before?" Spinner.

     "Unfortunately, yes..." Ryo groaned. The League turned their attentions to the privacy fence outside. On the other side of it, they could faintly hear a little boy calling, asking for his ball back. "Last time he did that, I yeeted his ball into the stratosphere! Of course he started crying and I got an ear full from his mom! So where's the ball? I'll just give it back to him."

     The league's eyes bulged a little, glancing between Ryo and the pile of ash left on the floor. It didn't take long for the teleporter to piece things together. "Hhhh." He rubbed his forehead. "You guys realize he's a kid, right?? And an adventurous one at that! He's going to climb over my fence again and, though he's a stupid little s###, is going to recognize all of you!

     "Crap!!" Twice jumped to his feet. "I say we all hide! I don't want to have to kill a little kid!"

     "Yeah, same.." Spinner joined him, though slower. Toga leaned even further into the back of the couch, reluctant to move again after she had found the perfect position of comfort.

     "I...'ll go buy another ball. You guys tell the others and stay out of sight!" Ryo vanished in that instant. Magne heard everything, already turning off the stove so she wouldn't burn anything while all of this was going down.

     "HELLO?.. Sir???" The little boy's call came again. A hand latched onto the top of the privacy fence, sending the league into a frenzy!! As the boy climbed over the fence, everyone scattered, finding places to hide.

     A little boy no older than four or five, sporting torn up jean shorts, an unbuttoned red vest of sorts, a yellow bandanna tied around his forehead, and a straw hat too big for his head plopped into Ryo's backyard. "Ouf!" He sprung back up quickly and brushed himself off. Then the boy cupped his hands together. "HELLO?! ANYBODY HERE!?" There was no response. Of course there wasn't!! "Oh no, I broke his window again!" The little boy panicked, jogging to the back patio of the villains' current headquarters. He yanked on the back door knob for a while, but eventually he deduced that the door was locked. So he crawled through the shattered window instead.

     The little boy started to look around for his ball, checking behind curtains and peering under couches. Twice was curled up in a ball in the corner, hiding himself under a singular gray blanket. He trembled, knowing that getting caught would likely mean having to put an end to this kid's life! So he REALLY didn't want to get caught!

     Spinner had somehow crawled up onto the ceiling and was hiding among the rafters up there. Toga was just too good at hiding! Not even the narrator knew where she was!

     The boy suddenly smelled something. He sniffed at the air, followed by a loud rumble in his stomach. The boy veered off course, making his way into the kitchen. Once in the kitchen, his legs stretched, allowing the small one to grow twice his original height! "Mmmm!" The boy remarked at the sight of freshly cooked grilled cheese sandwiches. "No.... Mmm.... Maaaaybe just one..." He followed that up by eating all five of the sandwiches that had been made so far in one fail swoop! "Oops!" He burped, shocked, like he didn't even realize he'd just inhaled all of them! At least, now, he was not so hungry.

     The boy shrank to his original size, relieving Magne, who had somehow shoved herself into the little space between the upper kitchen cabinets and the ceiling.

     He walked through the kitchen and turned into the entryway. The moment he exited the kitchen, the half-bath door creaked open, a disheveled Tomura hobbling out of there with a wad of toilet paper held under his nose.

     The two froze as they crossed paths in the hallway, making eye contact for an uncomfortably long stare down.

     "AAAAA!!! CREEPY GRANDMA!!!"

     "What?? Why you little--"

     "A-hahah! Yes, sorry, kid!" Ryo appeared behind the boy, placing his hand on the little one's shoulder. "Grandma's a little sick today. I promise you, she doesn't usually look quite this repulsing."

Tomura: ಠ⁠_⁠ಠ

     "A-anyways! You came in here for your ball, right? Well I found it! Here." Ryo handed the kid his newly purchased baseball. "You can go now, kid." His overly nice voice dropped in an instant, alerting the boy that he wasn't wanted here. The little one grabbed his ball and jogged around Ryo, away from the two villains in hiding.

     "Th-thanks!" The boy stopped at the back door after unlocking it for himself. He spun around, looking at Ryo bashfully. "Oh, and... I'm really sorry for smashing your window again..."

     Ryo smiled genuinely. "..It's okay, kid."

     "Here! I- I can help you clean up!" The boy jumped toward the mess, beginning to pick up shards of glass. Ryo hissed through his teeth, approaching with a cautious look on his face.

     "That's nice of you to offer.. but I don't want you to cut yourself... How about this? Follow me." Ryo slipped through the back door, beckoning the kid to follow.

     The League members started to relax one after another, slipping out of their hiding places to watch their new recruit from a distance through the windows.

     Outside, the Esper gave the kid a few tips on how to throw properly, especially working on his aim.

     "...Well who woulda imagined this?" Spinner folded his arms, resting them on the glass covered windowsill. "Guess this kid shouldn't be a problem anymore."

     "Awh, he's so cute though." Toga joined Spinner, knees on the couch same as him.

     "That kid ate our lunch.." Magne leaned in through the side of the window.

     "Eh, you can make more. I'm just glad we didn't have to hurt him!" Twice leaned through the other side of the window.

     The boy cheered after he succeeded in hitting a can Ryo had set up for him. While he celebrated, he caught several eyes staring at him in the house. He twisted his head toward the window, but there was no one there.

     Huh... Guess it was nothing.

     After the boy had shown obvious signs of improvement, Ryo pat the boy's hat and helped him back over the privacy fence. He then entered through the back door, sighing when at last he thought he was alone. He was not. The man grimaced upon noticing the funny looks of all those staring at him.

     "Stupid brat's gunna cost me a fortune.." He marched on up the stairs, problem resolved.

.

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In this story, One Piece is canonically just Luffy playing imagination with all his neighborhood and school friends. And he got the hat from his uncle before he disappeared, believed to be dead.