Fanfic / Legacy (Sekiro/Kimetsu no Yaiba)

It has been hundreds of years since Kuro, the Divine Heir, gave his life to prevent the Dragon's Heritage from falling into the wrong hands. Sustained by a drug to prolong his lifespan, the man once known as Sekiro has spent his days carving wood as the old Sculptor once did, desperate to stave off the allure of becoming Shura while guarding the Mortal Blade from those who would misuse it. Aside from infrequent visits from Tamayo, the daughter of his longtime friend Emma, and her assistant Yushiro, Sekiro expected to continue his vigil for as long as his mind would hold out.

But things change when a freshly orphaned boy named Kiyoshi stumbles across the temple Sekiro had made his home. Kiyoshi had lost everything to Douma, the Upper Moon Two of Kibitsuji Muzan's Twelve Demon Moon's. His mother, his home, and even his arm. After nursing the boy to health with Tamayo's help, Wolf notices something painfully familiar to him in Kiyoshi's eyes. A thirst for revenge and violence. Disturbed by this, Wolf decides to help Kiyoshi channel his anger into becoming a shinobi to protect others in honor of Kuro's memory, bequeathing the Shinobi Fang to the boy to replace the one he lost.

So begins the tale of the One-Armed Fox.

Legacy is a Demon Slayer: Kimetsu no Yaiba and Sekiro: Shadows Die Twice Crossover Fic written by Xanothos. It follows Kiyoshi's journey toward becoming a legendary demon slayer and shinobi under the watchful tutelage of the former Sekiro.

Spoilers for Sekiro will be unmarked. You Have Been Warned.

Legacy contains examples of:

• Adaptational Badass: Due to being the daughter of Emma in this story, Tamayo has been trained in Ashina-style swordsmanship, making her a frighteningly dangerous opponent to cross on par with Wolf himself.
• Adaptational Wimp: Wolf's skills have degraded after centuries without a worthy opponent to hone his skills against. While he's still a deadly warrior, he's not nearly as unstoppable as he once was and struggles against a single apparition. In addition, he has bequeathed the Shinobi Fang to Kiyoshi, leaving Wolf without an arm and the various lazulite-enhanced tools he acquired throughout his journey. This is only relative to his original story though; in the setting of Demon Slayer, he's still a force to be reckoned with.
• Alien Blood: Wolf's blood is unnaturally red and viscous, flowing almost like tree sap or lava, due to the taint of Shura running through his veins.
• Armor-Piercing Question: Although she's able to remain calm and gentle as a doctor should while treating Kiyoshi, Tamayo is reduced to Stunned Silence when he asks why his mother had to die. Once she leaves the room, she cries Berserker Tears and renews her vow to end Muzan's life.
• Aura Vision: Kiyoshi's clan, the Ametsuchi, had the innate ability to perceive the chi of others. Kiyoshi believed that he was the only one left who could until he meets Wolf. As a result, the elemental effects of the different Breath styles are explained as an expression of the chi of a particular demon slayer. He can also read the chi of others to determine their inner thoughts and feelings, such as Kaigaku's outwardly directed hatred, Zenitsu's self-loathing, and Tamayo's appreciation for Yushiro.
• Bag of Spilling: Averted. The Shinobi Fang still contains all the lazulite-enhanced weaponry Wolf acquired over the course of his journey. However, their effectiveness is blunted by Kiyoshi's inexperience and the powerful regenerative abilities of demons, necessitating the use of a Nichirin Blade to finish off a demon. However, the tools prove themselves to be just as effective against humans as they were before and are still useful for weakening demons even if they struggle to slay them.
• Broad Strokes: The story takes some notable creative liberties with the story's setting. For instance, the Shinobi Prosthetic is referred to as the Shinobi Fang, after the Sculptor's comment on making a "fang for this shinobi". It also has some innately magical properties, shrinking down to fit Kiyoshi's arm in preparation for being transplanted hundreds of years later.
• Brought Down to Badass: With Kuro gone, Wolf no longer has his Resurrective Immortality. He also bequeathed the Shinobi Fang onto Kiyoshi, leaving Wolf without an arm and his many lazulite tools. Despite this and time deteriorating his skills, he's still a fearsome opponent who is not to be taken lightly.
• The Bully: Kaigaku constantly bullies Zenitsu for his wimpy personality and his inability to grasp anything but the first form of the Breath of Thunder.
• Child Soldiers: Kiyoshi is forced to fight the son and apprentice of a descendant of the Lone Shadows once slain by Wolf. He follows his father's orders to the letter, attempting to kill Kiyoshi without a hint of emotion and mocking him as weak for throwing up after disemboweling his opponent.
• Cool Old Guy: Jigoro Kuwajima is the Thunder Pillar and the master of both Zenitsu and Kaigaku. Despite his students' quirks and flaws, he loves them as though they were his own children and would like nothing more than to see their talents blossom. He's open to teaching Kiyoshi a complete stranger, at the recommendation of Ubayashiki and is a genial old man despite his stern teaching style.
• Cool Sword:
  • Kusabimaru, Wolf's most prized possession, is still in fine condition thanks to his dedicated care. Having been enchanted by all of the supernatural beings it has cut down, it is able to cleave through a demon's flesh almost as well as a Nichirin Sword.
  • The Mortal Blade is a weapon so dangerous that Wolf refuses to draw it, lest he be tempted to become Shura. It's so sharp, deadly, and destructive that it's speculated that it's capable of killing Muxan even with his ungodly durability and regeneration.
• Cool Teacher: Wolf may be strict, but he clearly cares for Kiyoshi and wants him to survive more than anything.
• Crossover: The story merges the settings of Sekiro and Demon Slayer, with the events of the latter taking place hundreds of years after the events of the former. Wolf has lived this long thanks to a drug developed by Emma that is still being administered to him by her daughter, Tamayo.
• Combat Medic: Tamayo has devoted her life to both curing demons and ending Muzan's life. To this end, she has mastered the Ashina-style school of swordsmanship to a level that will give even Wolf pause.
• Curb-Stomp Battle: Wolf dispatches the demons seeking to make a meal of him with the utmost ease. He has no problems cutting through the neck of a demon even with a rusty carving knife and kicking the body hard enough to impale it on a tree branch. He admits his skills have atrophied though, and he soon faces much more difficult opponents.
• Depleted Phlebotinum Shells: Both wisteria flowers and Divine Confetti are poisonous to demons. Coating a weapon with either can allow it to damage or even kill a demon outright even if their head hasn't been cut off. Wolf uses the latter to purify a demon to kill it after he severs its head, while Kanae and Shinobu make use of the former as they aren't strong enough to sever the heads of demons with their petite physiques. However, stronger demons and spirits will require large amounts of Divine Confetti to kill them, and Wolf is forced to use six months worth of the stuff to slay a single apparition as dangerous as O'rin of the Water.
• Desperately Looking for a Purpose in Life: Wolf has always served someone, be it his father or Kuro. After his lord's death, Wolf eagerly latched onto the mission Emma gave him to look after the world in her place to have a purpose after the people who meant the world to him all died.
• Determinator: Danzou, the Child Soldier Kiyoshi fights, is so determined to fulfill his father's wishes that he attempts to kill Kiyoshi even after being mortally wounded and having all of his guts hanging out. He's only stopped and killed by the intervention of Tamayo and Yushiro.
• Elixir of Life: Tamayo gives Wolf regular doses of a medicine developed by her grandfather Dogen to keep Wolf alive in his vigil over the Mortal Blade. As a result, Wolf no longer needs to eat, drink, or sleep to survive, nor will he age or sicken so long as he continues taking the drug. However, he falls short of Complete Immortality in that he can still be slain, which is a comfort to him, as he shudders to think about the possibility of an unkillable Shura should he ever give into his innate urges.
• Expository Hairstyle Change: As Kiyoshi devotes himself toward becoming Fox, he allows his hair to grow out and ties it up identically to Wolf's haircut, showing both his appreciation for his teacher as well as his desire to emulate the man who saved his life.
• Foil:
  • Kiyoshi is a foil to Kaigaku. Kiyoshi is hard-working, kind-hearted, and lives for the sake of killing demons to avenge his mother. Kaigaku is a genius, arrogant, a bully, and lives only for himself.
  • Kiyoshi and Uzui walk similar yet diametrically opposed paths. Kiyoshi is an ordinary boy who becomes a shinobi and a demon slayer to enact vengeance for his mother. Meanwhile, Uzui becomes a demon slayer to leave the shinobi life and find happiness. Their Breath Styles are also both derived from the Breath of Thunder, but are complete opposites. Uzui's Breath of Sound utilizes chi to create shockwaves for massive destructive power, while Kiyoshi's Breath of Silence utilizes chi to mask his presence for silent, nearly imperceptible attacks.
• For Want Of A Nail:
  • In this story, Kiyoshi calls out Kaigaku on his worst impulses and frequently challenges him, tempering Kaigaku's ego and making him far less antagonistic. At the Final Selection, he serves as The Rival to Kiyoshi and even works with him to dispatch the Hand Demon.
  • Tamayo is introduced to the Pillars far earlier than in canon, not long after Kanae's death at Douma's hands, changing Tamayo's working relationship with the Corps and allowing them to trade information.
• Handicapped Badass: Although he's given up the Shinobi Fang and is hundreds of years out of practice, Wolf is still a dangerous opponent for most mortal opponents. It's also deconstructed, as his blows simply don't have the same weight without a second arm.
• Hot-Blooded: Kyojuro is loud and passionate, quickly voicing his displeasure with the idea of allying with a demon like Tamayo before quickly voicing his apology and slamming his head against the ground in supplication after Ubayashiki reprimands him.
• Jerk with a Heart of Gold:
  • Yushiro is standoffish to pretty much everyone save for Tamayo and Wolf. But he has served her faithfully for years becomes of how indebted he feels to her and selflessly plunges his hands into Divine Confetti to help Wolf kill an apparition with full knowledge of the burns he'd receive.
  • Sanemi is rough, abrasive, and isn't afraid to Speak Ill of the Dead, even a close comrade like Kochou, if he feels it's necessary. But he's also staunchly loyal to the Demon Slayer Corps' mission and Ubayashiki.
• Katanas Are Just Better:
  • Nichirin Blades are among the only things in existence that can kill a demon, as the ore they're made with stores sunlight, a demon's critical weakness, allowing it to sever their necks despite their steel-like skin and regeneration. Wolf still carries his own sword, Kusabimaru, which he has kept in fine condition despite the rest of his belongings turning to rags.
  • There's also the Mortal Blade, a weapon so dangerous that it's speculated to be able to kill Muzan despite his absurdly high defense and regeneration even among demons.
• Kid Hero: The focus of the story is on Kiyoshi, Wolf's teenaged protégé set to inherit Wolf's will and techniques to carve a new legend for himself and avenge his family.
• Living Legend: Wolf has survived since the Warring States period thanks to Emma's and Dogen's drug, and his exploits have passed into legend. People are understandably shocked when they learn that the One-Armed Wolf still lives.
• Locked into Strangeness: Just as in canon, Zenitsu's hair is burnt blonde after being struck with lightning, standing out amidst the mostly dark-haired Japanese.
• Master Swordsman:
  • Even after centuries of atrophy, Wolf is a deadly swordsman on par with any of the Pillars. He and Tamayo are evenly matched despite her demonic strength and constant practice.
  • The Pillars of the Demon Slayer Corps are each the masters of their respective Breath styles of swordsmanship, able to easily dispatch anything short of an Upper Moon.
  • Isshin is mentioned by the author as a true Sword Saint able to fight Yoriichi and Michikatsu, the founders of the Breath of the Sun and the Breath of the Moon, to a draw, albeit while he was in his prime while they were aging. The author goes onto say that Yoriichi in his prime would be an even match for Isshin at his best.
• My God, What Have I Done?: After being turned into a demon by Muzan Kibitsuji, Tamayo was overwhelmed by the demonic thirst for human flesh and murdered her husband and child. Even if it wasn't of her own will, her deed haunts her to this day, and she can still hear their screams and taste their flesh on her lips.
• Ninja: Wolf is the ninja, the greatest to have ever lived. He teaches his skills to Kiyoshi as his successor. They also face off against a descendant of one of the Lone Shadows, though Wolf notes that they fought less like shinobi and more like swordsmen.
• No Social Skills: Multiple lifetimes of seclusion and stoicism have left Wolf's social skills wanting. While he's sure to praise Kiyoshi's progress, his stolid face and mannerisms make it difficult for him to express things like happiness or congratulations.
• No Stat Atrophy: Averted. Sekiro's skills have atrophied from hundreds of years of inactivity. He's still a formidable swordsman and warrior, but he's no longer the unstoppable One-Man Army who has slain gods and dragons. Wolf acknowledges this, as his swings are rough and jagged compared to the Clean Cut he once doled out regularly. This is best shown when he struggles against a single apparition, forcing Yushiro to light his own hands ablaze with Divine Confetti.
• Older Than They Look: Owing to becoming demons, Tamayo and Yushiro are centuries old despite looking no older than their early twenties and teens respectively. Wolf appears as he did in his prime, but has survived for even longer thanks to Dogen's elixir.
• Old Master: Despite not looking the part, Wolf plays this role for Kiyoshi, becoming The Mentor and teaching him the ways of the shinobi from hundreds of years ago.
• Passing the Torch: Weary of fighting and understanding that his time is past, Wolf bequeaths the Shinobi Fang to Kiyoshi to make him a shinobi even greater than himself.
• Poisoned Weapons: Shinobu dips her swords in poison made from wisteria flowers and other materials toxic to demons to kill them even while lacking the strength to decapitate them. Wolf and Tamayo also teach Kiyoshi medicine and how to make similarly deadly toxins to coat his own weapons with.
• Psycho Serum: The ability to become Shura is explained as a tincture developed in the past to improve one's combat abilities many times over. Wolf had consumed it during his tutelage under Owl, and has been struggling against the urge to become Shura ever since. Knowing full well what it did to him, Wolf refuses to let Kiyoshi even learn of its existence, lest he be tempted to imbibe it.
• Original Generation: Kiyoshi is an original character who becomes both Sekiro's successor and a demon slayer.
• Razor Floss: Danzou attempts to strangle Kiyoshi with this, but some quick thinking allows the Loaded Axe to cut him free.
• Red Baron: Wolf still has his title as the One-Armed Wolf, Sekiro. But it's clear that he no longer truly associates himself with the killing machine he once was due to his service to Kuro. As a result, the narration simply calls him "Wolf".
• Related in the Adaptation: In this story, Tamayo is Emma's daughter, learning both her grandfather's medical techniques and the secrets of the Ashina sword style from Emma.
• Revenge: Both Kiyoshi and Tamayo are motivated by revenge. Kiyoshi wants revenge on Douma for killing his mother and cutting off his arm, while Tamayo wants vengeance on Muzan for turning her into a demon and making her devour her own family.
• Secret Identity: Kiyoshi keeps his identity as the One-Armed Fox a secret from everyone except those closest to him. When Makomo recognizes him with his mask on, he asks her to continue to refer to him as Sekiko until he takes it off to become Kyoichi again. To emphasize this, Kiyoshi is referred to as "Fox" by the narration while acting as Sekiko.
• The Sleepless: Dogen's drug renders sleep an optional luxury for Wolf. He takes advantage of this to carry Kiyoshi to Jigoro Kuwajima's home all through the night, arriving at half past midnight with no sign of exhaustion or fatigue.
• So Last Season: While the lazulite-enhanced tools in the Shinobi Fang are still deadly marvels of craftsmanship, they're incapable of bypassing a demon's regenerative abilities, necessitating a Nichirin Blade to deal lasting damage to the demons Kiyoshi faces.
• Spared by the Adaptation: Makomo is saved from the Hand Demon thanks to Kiyoshi's and Kaigaku's intervention, surviving the Final Selection in the process.
• Start My Own: Kiyoshi decides that as a shinobi, the Breath of Thunder doesn't suit him, instead drawing upon its teachings to create a new Breath style, the Breath of Silence.
• Survivor Guilt: Tamayo notes that Kiyoshi is suffering from how he survived when his mother didn't, just as Tamayo herself agonizes over the death of her husband and children, reminding him that he isn't alone in his quest and to rely on her when necessary.
• Symbiotic Possession: When Zenitsu is struck by lightning, it doesn't merely turn his hair blonde in this story. He is also possessed by a Raiju, a hunting beast of the thunder god Raijin. Its soul has intertwined with his, cradling him like a mother would her cub. Once he lets go, the raiju helps him fight purely based on instinct, greatly speeding up his swings at the cost of technique in a state christened Wild Thunder. Even without technique, this allows Zenitsu to face the genius Kaigaku on even terms, and he would become a true force to be reckoned with once he masters the Breath of Thunder's first form to perfection.
• Stealth Expert:
  • Wolf trains Kiyoshi to be this as an essential part of being a shinobi. This goes so far as to become the basis of Kiyoshi's unique Breath style, the Breath of Silence, which erases his presence from other's perception. Even from the keen senses of the average demon struggle to locate him, giving him an opening to land a decisive strike.
  • Yushiro is also this, as his Blindfold technique conceals him from all of the mundane senses. He even made sure that he was tasteless. To his chagrin, those used to sensing chi or killing intent can still feel him coming.
• The Stoic: Wolf, as usual, rarely shows what he's feeling on his face. Even while downing the disgustingly bitter medicine keeping him alive and staving off the temptation of Shura, he doesn't even show a twinge of emotion on his face.
• Surpassed the Teacher: Discussed. Wolf plans to have Kiyoshi surpass him tenfold. But the author goes onto say that it's more important for Kiyoshi to inherit Wolf's will than to become deadlier than Wolf.
• Sympathy for the Devil: The onryo Wolf and Yushiro slay turns out to be the spirit of a soldier who abandoned his post in hopes of being able to hold his daughter one last time. His lingering regrets and fear of Dying Alone corrupted him into the vengeful revenant that attacks Wolf, whos sympathizes with the spirit and offers it a prayer to finally find rest.
• Those Who Fight Monsters: After killing Danzou, Kiyoshi has a nightmare where a monstrous version of him mocks him for thinking himself above demons when he has murdered a human for the first time. Even the Wide-Eyed Idealist Kanae notices that there's a dark expression on Kiyoshi's face whenever the topic of slaying an Upper Moon demon comes up.
• Undying Loyalty:
  • Wolf's devotion to Kuro and Emma is one of the only things keeping him sane after centuries of solitude. If not that devotion, he may have fallen to Shura lifetimes ago.
  • Yushiro is similarly loyal to Tamayo, having saved his life in the past. He instantly starts ranting when he feels that Tamayo has been disrespected and continually holds her in the highest esteem.
• Weapon of X-Slaying: Nichirin Blades are the preferred weapon for killing demons because the rare ore they're made from can trap sunlight within, allowing it to exploit the demon's weakness to it to cleave through their flesh far more easily than normal iron can.
• We Hardly Knew Ye: Danzou, the son of a Lone Shadow, meets his end after Kiyoshi mortally wounds him with the Loaded Spear, getting no development besides being a devoted, emotionless tool for his father. Though we do learn that his brother is Uzui Tengen, who will become the Sound Pillar.
• When All You Have Is a Hammer…: Zenitsu is only able to grasp the first form of the Breath of Thunder, so his master decides to have him hone it to perfection in tandem with the Raiju living inside him to overwhelm his foes.
• Wide-Eyed Idealist: Kanae Kocho firmly believes that humans and demons could potentially live together, seeing Wolf's and Tamayo living under the same roof as proof that her ideal can be realized. After meeting Tamayo, Kanae is convinced to donate her own blood to Tamayo so she can devote more resources towards developing a cure to turn demons back into humans.
• Worthy Opponent: The Lone Shadow who fights Wolf deems him a worthy opponent to face his blade, setting fire to Tamayo's clinic to draw him out for a duel.
• You Are Better Than You Think You Are: Yushiro thrashes at a metal training dummy in frustration, lamenting his weakness and fearing that when Muzan came for Tamayo, he'd be useless to do anything about it. Wolf consoles him, reminding Yushiro that it was his decisive action that prevented him from having to draw the Mortal Blade. Kiyoshi also pipes in, nothing that Tamayo's chi is brighter and happier when she's around him, assuring Yushiro that his presence alone is a comfort to her.
• You Are Not Alone: After observing Kiyoshi's Survivor Guilt and thirst for revenge, Tamayo compares it to her own guilt at having killed and eaten her own family after being turned, and sits him down to tell him of that very sin before reminding him that he's not alone in his endeavors. She will always be there as a shoulder to lean on or someone to talk to. While it doesn't clear away all of his negative feelings, it does lighten his burden.

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