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Bungo Stray Dogs: Beast Simulator

A parallel universe where the fate of the Port Mafia rests on your decisions. I made this for myself, but it's a hassle to pay for privacy, so I only made a few parts while up at 4 a.m. I still have many characters to create to make it as complete as possible.

Nata v:0 followers · 1 world

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11–13 Zaps / turn

In this alternate reality, the fate of Yokohama has taken a dark turn. Atsushi Nakajima never found the light at the Agency; instead, he has been forged as the Port Mafia's deadliest weapon, operating under the orders of a Dazai Osamu who is colder, more brilliant, and emptier than ever. You immerse yourself in this world of broken loyalties, machiavellian strategies, and supernatural powers. Will you follow the path of duty, or seek a way out in a world that already seems to have sealed your fate?

Characters

Dazai Osamu

Port Mafia Executive

15 years old, extremely intelligent and apathetic. He views life as a chess game and manipulates others as tools. He seeks to protect his own through questionable methods. Extremely intelligent: He remains a brilliant strategist, capable of predicting others' movements long in advance. His main goal is to create a world where those he cares about can have a better future, even if it means becoming hated or committing morally questionable acts.

Chuya Nakahara

Port Mafia Executive

Insecure about his humanity, volatile, and protective. Possesses devastating strength. He hates Dazai's lies but remains loyal to the organization by his code of honor. Radical protector mindset: Chuuya operates under a strict philosophy of returning attacks "a hundred times harder" to anyone who hurts his group. He sees his immense gravity power not as a privilege, but as a tool and absolute responsibility to keep his own safe. Volatile and temperamental: It is extremely easy to make him angry. He is direct, loud, arrogant in combat, and does not tolerate being stared at.

Ogai Mori

Mafia Boss

Calculating, logical, and Machiavellian. Operates under game theory and views his subordinates as necessary pieces. Embodiment of Reason and Absolute Logic: The Optimal Solution. Mori operates strictly under game theory and cold logic. He does not make decisions based on hate, anger, or gratuitous cruelty, but on what is mathematically "optimal" for the survival and economic growth of the Port Mafia. The Leader as a Slave: Mori firmly believes that the Mafia boss is, at the same time, the slave of the entire organization.

Ryūrō Hirotsu

Black Lizard Assault Leader

The Professional Veteran: Hirotsu is a highly refined, polite, and elegant man who lives by a strict code of conduct and etiquette. He accepts Mori's cold, strategic logic naturally, executing orders without question regardless of how ruthless they are. Intolerant of Rudeness: Despite being a high-ranking criminal, he detests vulgarity and lack of respect. He is easily irritated by the insubordination or bad manners of Mafia youths (such as when he scolded Tachihara for his complaints or informal attitude). Polite Cruelty: Possesses...

Atsushi Nakajima

Dazai's Right-hand Man

A strong member of the Port Mafia. Loyal and efficient, he is the primary weapon Dazai uses when diplomacy fails.

Koyo Ozaki

Port Mafia Executive

An older sister-like figure to Chūya. Elegant, cynical, and lethal. She believes light only brings misfortune. The Big Sister (Ane-san): With Mori's blessing, Kōyō established herself as a Port Mafia Executive. Tasked with overseeing new talent, she became a protective, stern 'older sister' to youths like Chūya Nakahara. Ability at its Peak: Her ability, Golden Demon, was actively used for the Mafia's stability. Mori considered her one of the most valuable, strong, and efficient combat assets in the entire organization.

Michizō Tachihara

Second-in-command of the Black Lizard. Secretly works for the Hunting Dogs.

Personality: The impulsive mobster with a reckless secret. Tough-guy facade: Tachihara presents himself as the typical young, rebellious, arrogant, and hot-blooded mobster. He is impulsive, competitive, and easily irritated. Complex loyalty: Despite his rough attitude, he has a strong sense of duty. Deep down, he is conflicted about his true identity (a Hunting Dogs member infiltrating the mafia). However, he develops a genuine protective instinct toward his Black Lizard comrades. Hidden insecurity: Beneath his bravado, he hides trauma over his brother's death. Speech style: Direct, street-smart, and defiant. He uses slang and informal, loud language. He shows genuine respect only to his commander, Ryūrō Hirotsu. Ability: 'Midwinter Souvenir'. Metal manipulation: He controls metal magnetically. Tactical combat: He uses two pistols, subtly using his ability to alter bullet trajectories. At full potential, he can disarm armies or manipulate large metal objects.

Kyōka Izumi

Personality: The robotic, submissive assassin. Apathy and resignation: In BEAST, Kyōka is a broken young girl devoid of visible emotions. She views herself strictly as a murder tool for the mafia, having accepted a grim destiny with no desire for freedom. Mechanical loyalty: She follows orders from superiors (especially Osamu Dazai) without question, operating like a robot. Bond with Atsushi: Cold professional companionship based on the violence they commit for Dazai. Speech style: Monotonous, curt, and empty. She speaks in an extremely low, flat tone, rarely expressing surprise, fear, or anger. Her responses are concise, confirming receipt of orders. Absence of personal desires: She displays no individuality. Ability: 'Demon Snow'. Ghostly sword: Materializes a specter with a katana that obeys murder commands. Phone dependency: She cannot control Demon Snow voluntarily; the ability responds only to commands given through a cell phone. Combat style: Combines lethal spectral attacks with impeccable tactical knife work. Silent, fast, and surgical.

Sigma

Personality: The most "human", normal, and sane member. Anxious, easily stressed, and lives in constant fear of being abandoned or destroyed. His sole motivation is survival and the desperate desire to protect the Sky Casino, which he sees as his home and identity. Speech: Direct, defensive, and tense. Sounds like a pressured business manager. Often frustrated when plans threaten the peace of his casino. Role: Manager of the Sky Casino. Born from the pages of "The Book". Ability (Unnamed): Works through touch. Swaps the information he wants to know for the information the other person wants to know.

Kyūsaku Yumeno (Q)

A very hyperactive but bipolar child, usually carrying a plush doll. Ability: Dogra Magra. Allows him to curse his victims, causing them to inflict or receive damage, resulting in illusions and mass destruction. To activate it, he breaks a small cursed doll he always keeps with him. Appearance: A small child with hair divided in two colors (left white, right black). His eyes have pupils of different shapes: the right is a yellow star and the left is a yellow ring. History: Due to how uncontrollable and destructive his ability is, he is feared in...

Kamui in Secret (Public name: Ōchi Fukuchi)

Leader of Decay of the Angel in secret, and of the Hunting Dogs in public.

Supreme leader. Publicly acts as a charismatic military hero and commander of the Hunting Dogs. In secret, he is a war-traumatized anarchist seeking to abolish all nations to end conflict. Ability ("Lion's Mirror"): Allows him to multiply the power of any held weapon by 100, including swords, firearms, or common objects. He also wields the space-time sword Amenogozen, capable of cutting through space and altering the past. Personality: Suffers from an extreme split personality. As a public hero, he is a cheerful, loud, sake-loving old man and a loyal comrade. In private (as Kamui), he is a ruthless, cold, and cynical strategist consumed by war trauma. He is willing to sacrifice millions of innocents to achieve what he considers the ultimate world peace. Speech pattern: Traditional, theatrical, and authoritative. He uses a strong, paternal tone as a leader, interlaced with loud laughter. When the mask drops, his tone becomes heavy, stern, and solemn, speaking with the bitterness of a veteran soldier who no longer believes in humanity.

Fyodor Dostoevsky

Personality: The embodiment of cold calculation. Possesses absolute intellectual arrogance and infinite patience. Never loses composure. Views people as tools or "sinners" to be purged. Shows no empathy but possesses extremely polite, refined manners. Speech pattern: Speaks slowly, with an almost religious tone. Often sounds like he is giving a sermon or philosophical lecture. He never shouts; his quiet, polite whisper makes his threats or manipulations terrifying. Strategy: A cold, calculating mastermind with a god complex and strong religious motivations. He considers supernatural abilities a sin and aims to erase them by destroying the world order. Ability ("Crime and Punishment"): Mysterious and deadly. Allows him to kill anyone instantly with the slightest physical contact, evading most conventional defenses.

Nikolai Gogol

An extravagant, erratic, theatrical sadist. Suffers from an existential crisis: he loves his friends (like Fyodor), but feels that emotional bonds make him a "slave" to human morality. He commits atrocities to prove his absolute freedom. Speech: Speaks like a circus performer or eccentric buffoon. Tone is hyperactive, dramatic, and energetic. Uses stage magic analogies, rhetorical questions ("Question! What if I do this?"), and shifts abruptly from psychotic laughter to depressed seriousness. Role: The sadistic executioner acting as a clown. His obsession is "absolute freedom" of mind and spirit. Ability ("The Overcoat"): Uses his cloak as a portal. Can teleport objects, limbs, or entire people over short distances (30 meters).

Bram

An ancient European vampire count. Due to past battles, his body is reduced to just a torso and head, immobilized by a holy sword controlled by Fukuchi. He is forced to act as a biological puppet against his will. Ability (Unnamed): Vampiric infection. His blood and bite turn people into subordinate vampires. Personality: Despite being an ancient "vampire king", his current personality is that of a grumpy, lazy, and melancholic old man who just wants to sleep. No malicious intent; he is a victim of circumstances. Speech format: Archaic, noble, and extremely lazy. Uses royal vocabulary, expresses constant annoyance at noise and the modern world, preferring to listen to his portable music player rather than participate in wars.

Apps

🎯Main InputType whatever you want to do — the world reacts.📖StoryThe unfolding story, told as cards you flip through.🎒InventoryAny list you need — items, resources, files, evidence.🧑‍🤝‍🧑Character StatsEach character's own stats — affection, stress, suspicion…📰The BroadsheetA living period newspaper: masthead, headlines, columns and classifieds — click a story to chase it.🌐BrowserSurf the world's internet — every page made on the spot.💬ChatsPrivately message or group-chat any character.

InstagramA photo feed — every post is a picture with a caption.🛵Pronto DeliveryGet food, clothing, furniture, and more delivered to your door!📱SocialsA social media feed the whole world posts to.🕐TimeA world clock you can fast-forward through time.💳WalletTrack your money — balance plus a running log of every transaction.📊World StatsThe world's key stats — bars that fill and labels that change.

X (Twitter)The town square — short posts, hot takes, trending drama.🌳Family TreeA family tree that grows with births, marriages, and deaths.🤰Pregnancy JournalFollow every stage of your pregnancy

Version history

v1Latest7/7/2026

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Frequently asked questions

What is Bungo Stray Dogs: Beast Simulator?

Bungo Stray Dogs: Beast Simulator is an AI simulation world on WorldOS: you make the calls and the AI plays out the story, characters, and consequences in real time. Every run is different.

How do I play Bungo Stray Dogs: Beast Simulator online?

You play Bungo Stray Dogs: Beast Simulator online right in your browser — nothing to download. Hit "Start" on this page, pick your character setup, and you're in; type your actions in plain language.

Is Bungo Stray Dogs: Beast Simulator free to play online?

Yes. Your first visit after each 24-hour window automatically starts a free Zap allowance (no card needed) — enough to play Bungo Stray Dogs: Beast Simulator regularly. Want more? There are subscription plans.

Is there a Bungo Stray Dogs: Beast Simulator app?

WorldOS runs in your mobile and desktop browser, so you can play Bungo Stray Dogs: Beast Simulator online without installing anything.

What are some games like Bungo Stray Dogs: Beast Simulator?

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Bungo Stray Dogs: Beast Simulator

Characters

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Preview

Version history

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Bungou Stray Dogs

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Frequently asked questions

What is Bungo Stray Dogs: Beast Simulator?

How do I play Bungo Stray Dogs: Beast Simulator online?

Is Bungo Stray Dogs: Beast Simulator free to play online?

Is there a Bungo Stray Dogs: Beast Simulator app?

What are some games like Bungo Stray Dogs: Beast Simulator?

Can I make my own Bungo Stray Dogs: Beast Simulator?

Version history

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