[Completed!] Osomatsu-san: Our 7th Brother?! (Fanfiction Story Movie)

Chapter 1: Our Seventh Brother?!

The Matsuno household was unusually quiet, a rare and almost eerie calm settling over the normally chaotic space. The only sound that lingered was the ticking of the clock on the wall—a slow, steady rhythm that felt out of place. There were no screams, no crashes, no sarcastic shouting matches. Just the kind of peace no one in the family had asked for.

Osomatsu lay slouched across the couch, limbs sprawled and mouth half open as he lazily picked at his ear.

Osomatsu (bored): Ugh, this is so boring.

His eyes wandered to the ceiling, where a barely visible cobweb trembled slightly from the soft breeze slipping through the window. The stillness was driving him crazy.

Sitting cross-legged on the floor, Karamatsu gently strummed his guitar, eyes half-lidded. Each note rang out softly, the chords melancholic and smooth, as if he were composing a love song no one else could hear. Every few strums, he adjusted the tuning and nodded in self-approval.

Choromatsu sat upright in an armchair, clutching his phone tightly. His eyes were locked on the screen as he scrolled through an endless stream of idol group updates.

Choromatsu (muttering): Another livestream tomorrow? How do they expect fans to keep up?

Lying flat on the floor with a familiar tabby curled on his chest, Ichimatsu idly scratched behind the cat's ears. His vacant stare remained locked on the wall. Occasionally, he murmured something incomprehensible. The cat meowed softly in return, their conversation lost in a language only they seemed to understand.

Meanwhile, Jyushimatsu bounced a baseball off the wall with relentless rhythm. The thunk-thunk-thunk of it rebounding filled the room like a metronome. His smile was unwavering, eyes lit with the simple joy of movement.

Todomatsu stood by the mirror, frowning as he examined his hair under different angles.

Todomatsu (annoyed): No, no, no. This lighting is terrible.

Even if he wasn't taking selfies today, he refused to let his reflection betray anything less than perfection.

The tranquility lasted a few more seconds—until a familiar voice cut through the air.

Totoko (shouting from the street): Fresh fish! Fresh fish! Get your fresh fish! Everything is 50% off today!

The brothers all turned toward the open window, the volume of her voice snapping them out of their respective distractions.

Osomatsu (sitting up suddenly): Did you hear that? Totoko-chan's got a sale going on!

Choromatsu (perking up): Fifty percent off? That's—

Osomatsu (grinning): Forget the fish, guys. Let's hit the pachinko parlor! Who's in?

Karamatsu (smirking): Pachinko sounds good. Let's make it worth our time.

Jyushimatsu (pumped): Pachinko! Pachinko! Let's gooooo!

Todomatsu (shrugging): I guess I'm in. But don't expect me to carry you losers.

Ichimatsu (dry): Whatever. Anything's better than sitting here.

Choromatsu (sighing): Fine. But if we lose, it's coming out of your share, Nii-san.

Just as they began shuffling to gather their things, their mother suddenly burst into the room, her eyes bright with excitement.

Matsuyo (excited): Boys! Drop everything! I have a huge announcement!

The brothers froze mid-step, turning toward her with various degrees of curiosity and irritation.

Osomatsu (mildly annoyed): What is it, Mom? We were just about to leave.

Matsuyo (beaming): This is more important. Meet your new brother!

She stepped aside, and a boy slowly entered the doorway. He looked nervous—clearly out of place, yet trying his best to stay calm. His black no-zipper hoodie hung slightly oversized, the sleeves nearly covering his hands. Brown shorts fell just above his knees, and long white socks stretched neatly up his legs. He clutched the edge of his hoodie with one hand and adjusted his glasses with the other. His smooth, dark hair sat neatly over his forehead, and his hazel eyes darted quickly over the group. With a soft, awkward wave, he introduced himself.

Haruto (nervously): H-hi... I'm Haruto. Your... your adopted brother.

The room dropped into stunned silence. The six brothers stared, mouths slightly agape, processing the words.

Osomatsu (blinking hard): Wait, wait, wait... adopted brother? Seventh brother? Are you kidding me?

Karamatsu (raising an eyebrow): Another brother, huh? That's... unexpected.

Choromatsu (panicking): This has to be a mistake! Mom, are you serious? We're already barely functioning as six! Seven is—no, no, no, this can't be real!

Ichimatsu (dry): Great. Another person to steal my snacks.

Jyushimatsu (rushing over): HI, HI! Do you like baseball?! Do you want to play baseball with me?!

Haruto took a small step back, his cheeks turning a faint pink under Jyushimatsu's sudden enthusiasm.

Haruto (startled): Uh... I guess? I mean, I've never really—

Todomatsu (studying him): Hmm... you're kind of awkward, huh? That's not a bad thing. But are you sure you'll fit in with us?

Haruto adjusted his glasses again, his expression softening into a shy smile.

Haruto (determined): I-I'll do my best! I know this is sudden, but... I really want to get along with you guys.

Osomatsu (grinning): Get along, huh? Well, Haruto, it's not that simple. We've got rules in this family.

Haruto (confused): Rules?

Osomatsu: Yeah. Rule number one: You have to survive a day with us. And trust me—that's not easy.

The brothers all exchanged mischievous looks. Whatever this new brother thought he was getting into... he had no idea.

Haruto (nervously smiling): I'm up for it! Bring it on!

Matsuyo (clapping): Perfect! I'll leave you boys to get acquainted. Be nice to your new brother!

As their mother left the room, the energy shifted again. The brothers slowly began circling Haruto, eyes gleaming with curiosity, playful smirks spreading on their faces.

Choromatsu (curious): So... what do we do with him first, Nii-san?

Osomatsu (smirking): Oh, I've got a few ideas...

And just like that, the peace that once filled the Matsuno household vanished. The real chaos was about to begin.

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Hi everyone!
This is MiroPH! I've been a big fan of Osomatsu-san since 2021. I know I'm late to the party, but I think it's finally time to write another anime fanfic—something different from just Doraemon stories. I'm really excited to share this new journey with all of you, and I hope you enjoy the ride with our chaotic Matsuno brothers... plus one new face!

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