Fanfic / Lusus Naturae

The size of a cargo truck, with black skin that seemed like rock and filled with teeth-like spikes. And it had eyes. Lots and lots of eyes.

"What's the worst that could happen?"

—Unknown (Forever remembered as the biggest idiot in the Omniverse)

Lusus Naturae, Latin for "Freak of Nature", is a Sword Art Online Fanfic by SaintInfernalNeos.

One night, when Kirigaya Minetaka was driving home after spending New Years with his wife's, Kirigaya Midori's, parents, a thunderous 'Boom' echoed through the mountain road.

Against better judgment, they proceeded to investigate with the excuse that someone might be hurt, despite the fact that there shouldn't be anything around for kilometers.

When they came across a strange 'pod', they knew they should have walked away. But, at that moment the pod proceeded to eject a confused and weird-eyed little kid. He seemed harmless enough, and he made their daughter laugh, so really, bringing him home couldn't hurt, right? After all, what's the worst that could happen?

...as many people, like Kayaba Akihiko, would find out years later when meeting 'Kirigaya Kazuto', quite a lot of hilariously sinister things, actually.

Kazuto also runs into many of our heroines IRL before Sword Art Online even launches, which has varying effects on each of them.

The fanfic can be found here. It was completed as of July 13, 2019.

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Lusus Naturae provides examples of:

• Adaptational Heroism: PoH. Yes, THAT PoH, who helps rescue Kirito from the Ocean Turtle and even Takes the Bullet for the others. Granted, he tries to play it off as an Evil Versus Oblivion scenario.
• Adaptation Personality Change: Shino, due to Kirito being at the post office during the incident that marked her in Canon, and disarming the robber in a very Alien way. This Leads Shino to become obsessed with aliens and conspiracies. Kirito is this too due to his alien nature.
  • Same goes for Yui. As her functions were never disabled, she never loses her memory or reverts to a child-like mentality, maintaining a fairly mature disposition in her capacity as Kirito's personal counseling AI. As a result, she is completely unable to deal with Kirito's Cloud Cuckoo Lander mentality and repeatedly begs to be reassigned to no avail. Quite the far cry from being his Happily Adopted virtual daughter.
• Adaptational Antagonism: Kikuoka and the Japanese Government in general become the main antagonists in the last stretch of the story, but mostly because they're trying to react to what they perceive is an alien invasion and find themselves wholly unprepared for the full ramifications of their actions.
• And I Must Scream: The device used by Kikuoka and his troops to contain Mirai is this, a reverse-engineered Fulldive device that uses the Medicuboid and Nervegear's ability to shut down its wearer's physical sensations and motor functions to keep them imprisoned in their own body.
• Armor-Piercing Question: Kikuoka accidentally asks one to Kirito in Chapter 19 without realizing it:"Why do you smile." The results...arent pretty...
• Ax-Crazy: Eiji, becomes clearly unhinged when he decides to join up with Kikuoka to get back at Kirito and Mirai.
• Babies Ever After: Yuna announces that she is pregnant in the epilogue to Kirito's joy and the other girls' jealousy
• Becoming the Mask: Argo only approached Kirito in the SAO Beta because she realized how much potential the hopelessly naive newbie had that anyone pretending to be his friend could easily exploit--so she did. By the time the beta was closing down, sympathy, genuine affection and a healthy dose of guilt led Argo to truly become his friend and fall in love with him.
  • Kirito himself. "Kirigaya Kazuto" was the last-ditch attempt by the experiment's original self to find meaning in life, any meaning at all, drowning in despair and contempt for life as it was. It is in learning to be human and allowing love to bloom in his heart that "Kirito" eventually overpowers and subsumes the "Hate" persona, fully becoming "Kirigaya Kazuto".
• Being Tortured Makes You Evil: Eiji was captured and tortured by Mirai to get information on Kirito, caving in when the latter threatens Yuuna. This, combined with the revelation that Yuuna was not only fully aware of, but also fully accepting and in love with Kirito, causes him to snap, and become Kikuoka's attack dog.
  • This is also essentially why Kirito's original self came to hate all life and desired to end everything; being subjected to countless experiments and trials under the Tryum led to despising life, believing living brings nothing but pain, so in ending life everywhere, no one would have to suffer living anymore. It is ultimately love that allows Kirito's human self to overcome his monster self and stop the apocalypse.
• Big Damn Heroes: Subverted. Suguha and Kage's attempt to save Kirito from Wayrum's capture fails.
  • Played straight when the mutated Sleeping Knights save Kirito's family Mirai included from government capture...though it doesn't look that way at first.
• Bio-Augmentation: Upon capturing Mirai, Kikuoka and his scientists use pieces of her genetic material to turn Eiji into a hybrid Super-Soldier who easily repels a group of Tryums with lethal results.
  • Kirito can do this himself by injecting his DNA into another living being. It can lead to partial, localized augmentation (such as Suguha's severed leg) or full-on genetic conversion into a hybrid being similar to himself (like what he does to Kage-chan the crow, or the Sleeping Knights).
• Bizarre Alien Biology: Kirito and every species he ever ate. The Tryums as well.
• Blue-and-Orange Morality: Kirito, at first. He gained enough knowledge of human norms to eventually become a Cloud Cuckoo Lander.
  • Mirai is basically what Kirito would have been like without having developed a relatively human mindset to reign him in.
• Brother–Sister Incest: In-name only, since they're completely unrelated in this story, but Suguha is very much into her adopted brother. Kirito actually reciprocates but had no idea how to say it until prompted to be as direct as possible with his feelings.
  • Mirai is murderously, obsessively in love with her brother, and will kill anyone who is close to him, including and especially those who try to "steal" her spot as Kirito's sister.
• Butt-Monkey: Waryum the Tryum.
• Bunny-Ears Lawyer: PoH is an actual hitman in real life, he clearly enjoys his job far too much, and the fact he's willing to entertain absurd requests from his clients in the middle of a job says a lot about his standards; but he's also very efficient and still a professional; if the job description says "help bust out this weird kid I play online games with who turned out to be an alien from a top-security government facility while escorting his harem of schoolgirls, his mom and a bunch of alien abominations", then by God he's going to do it and he's going to love doing it.
• Cloudcuckoolander: Kirito has...a unique thought process.
• Dark Is Not Evil: He's weird, but Kirito is still a pretty nice dude all around.
  • This eventually extends to the hybrids as well. Even Mirai comes around eventually, but not Eiji. PoH is more of a Token Evil Teammate though.
• Didn't Think This Through: Upon rearranging the DNA of the Sleeping Knights to save them, the others point out that they now have no other place to go or any supplies since he snuck them out of their hospitals. Fortunately, Kirito manages to arrange for Kayaba to use his newfound wealth to cover their needs and supplies.
• Eldritch Abomination: 'X-K0940', or Kirigaya Kazuto, is a product of an Alien Experiment to 'enhance' an egg that survived being exposed to a very specific type of radiation from a bomb they dropped on its native planet, for no reason other than to win a bet.
• Emergency Transformation: When Kage-chan the crow is fatally injured, Kirito transforms her into a hybrid of a crow and himself in order to restore her life. He later does the same to the Sleeping Knights in order to save them from their various terminal conditions, though his lack of foresight in this one nearly bites him very hard in the ass afterwards.
• Everyone Has Standards: For all his moral scruples Kikuoka finds Eiji's bloodthirsty nature disturbing and has an Explosive Leash placed on him.
• Exotic Eye Designs: Kirito's real eyes are described as 2 red slits with golden sclera filled with black veins.
• Extra Eyes: In his Non-Human form, Kirito has eyes all over his body. They also have Hellish Pupils.
• First Kiss: Between Kirito and Yuuna in chapter 6. ^note Chapter 6: InHuman Morality
• For Science!: Half the reason Kirito was experimented on by the Tryums.
  • It Amused Me: The other half.
• Friendly Enemy: Due to SAO not being a death game in this story, Laughing Coffin is just a normal bunch of player-killers instead of actual murderers like in canon. Consequently, they give even less of a hoot about the consequences of player-killing and PoH himself takes to the field. Consequently, he regularly has scraps with Kirito and sort-of befriended him after being bested multiple times, respecting his prowess and believing that the two aren't so different. By the end of the story, he and his guild are seemingly at worst Token Evil Teammates, if not true comrades of the protagonists.
• Giant Flyer: Kage-chan and her spawns' hybrid forms are large enough for people to ride them. In the epilogue they grow to be large enough to be capable of space travel and attack starships.
• Half-Human Hybrid: Kirito can inject people with his DNA to give them powers and abilities similar to his own. Like when he does so to The Sleeping Knights to cure them of their terminal illnesses and Suguha. Eiji was also injected with some to become a Super-Soldier.
• Healing Factor: Kirito has a VERY potent one. Waryum's species has one as well, though not to the same absurd degrees.
• Heel–Face Turn:
  • Waryum more or less becomes another of Kirito's bunch after their initial misunderstandings are cleared.
  • Before him, Kayaba Akihiko was convinced to avert the death game entirely when made to see that between him and a bona fide Eldritch Abomination (Kirito), the real monster was himself.
  • Mirai becomes a lot easier to get along with after being made to learn some humanity through quite a lot of hardships. It helps she joins up with a bunch of people (mostly girls) who all love her brother as well.
  • PoH himself after being hired to help save Kirito from the government, though he wasn't quite an antagonist in this continuity. His whole guild follows in the epilogue.
  • The unusually thoughtful Pibap defects from the Tryum at the last minute and brings with him exactly what Waryum needs to stop Kirito from dying, being moved and intrigued by the concept of a real family that Waryum claims he learned by living among humans.
  • Kirito himself. First, the souls of all beings he consumed during his time as an experiment were soothed after he allowed their rage to mix with his own and drive him out of control. After, it was his [Hate] persona, the original personality of X-K0940, which came to hate life itself. By embracing both the good and the bad that came with living, nurtured and tempered with the love he discovered, [Hate] is soothed and stopped short of executing the apocalypse. Kirito is now the dominant personality, with [Hate] waiting in the wings should something truly require it to resurface again.
• Higher-Tech Species: The aliens known as 'The Tryums' are this. In fact, their tech is way beyond any other race in the universe. It and their powerful Healing Factor are the only things keeping them ahead, because otherwise they show a crippling lack of common sense as a species. Or remorse. Or impulse control. Or the ability to care about the consequences of their actions. Basically, every race who has dealt with them despises them simply because, by and large, they're a bunch of dicks.
• Human Aliens: Kirito is this most of the time due to Voluntary Shapeshifting. As a bonus, his internal physiology is normally human due to him thinking of himself that way.
• Humanity Is Infectious: Being raised by humans has clearly affected Kirito's personality. Waryum also admits to being affected as a result of hiding amongst humans for so long.
• I Have Your Wife: Kikuoka attempts to cajole Kirito into this by using his loved ones as leverage, threatening that with their involvement in covering him up, it would be easy to ruin their careers (In the case of Shigemura and Midori) or future prospects (In the case of his loved ones who are still in school.
• I Just Want to Be Normal: Downplayed, but, to a degree, Kirito is interested in wanting to be normal which is why he became interested in SAO in the first place.
• Instant Expert: Thanks to his biology, Kirito was capable of singing rather decently on his first try in Chapter 1 ^note Chapter 1: When Monster met Dreamer…, which provoked Yuuna to declare him her singing rival.
  • In actuality, Kirito cannot master anything on his own; he can only learn to imitate what someone else does first. Therefore, Yuuna cannot "beat" him on their singing contests because Kirito will always sing just as well as she does, but Kirito will never "win" either because he can only sing as well as Yunna does.
• It Can Think: Waryum is shocked by the fact that Kirito is not only capable of speech and thought, but that he can even dream and have nightmares.
• Kryptonite Factor: A very specific genetic sequence attuned to Kirito's exact genome can completely bypass his Healing Factor and trigger his body into destroying itself with no way for him or anyone to stop it, save for the Tryums themselves. The only being in the universe with the knowledge of this sequence is Waryum himself, but he holds off on it because he can't bring himself to kill Kirito after having seen his honest and gentle nature, even knowing how potentially dangerous he is.
• LEGO Genetics: An ability Kirito discovers when trying to save a crow, later named Kage-chan, and later uses to save the Sleeping Knights. Also uses it to fly, shoot plasma from a head-arm, create weapons out of his bones, morph his arm into a deadly bio-blade, etc.
• Make It Look Like an Accident: Sugou tries to make it look like Kirito got drunk in an underage indiscretion and walked off a building to his death in order to remove him from Asuna's life. What ends up happening is that Kirito makes it look like Sugou (and his paid goon) got drunk while driving and (non-lethally) crashed. Needless to say, this "scandal" removes him from Asuna's life entirely, and it prompts Kirito to propose to Asuna right afterwards.
• Memory Gambit: Turns out living for centuries being experimented on and tortured isn't good for anyone's mental stability, even a nigh invulnerable alien. When he escaped from the Tryum facility, he decided to voluntarily forget the majority of his memories and live as a (mostly) normal human in a desperate attempt to see if he could have a life worth living. It worked.
• Never Gets Drunk: Kirito due to his Eldritch Abomination physiology. Subverted as he does get drunk courtesy of PoH and Sinon.
• Nigh-Invulnerable: Kirito is this thanks to his very potent and adaptive Healing Factor. Waryum theorizes that the only way to put him down permanently would be to toss him into the sun.
• Nightmare Fetishist: As it turns out, Yuuki has a fascination with tentacles. Kirito can manifest countless tentacles. She doesn't even bother hiding how much she enjoys being manhandled by them whenever circumstances make it happen, to her beleaguered older sister's chagrin. A Noodle Incident discussed in the epilogue eventually reveals Yuuki got to live her fantasies the one time Kirito got drunk off his ass.
• Noodle Incident: Two
  • An accident involving Waryum and Several X-K0 specimens caused the creation of a supermassive black hole in the center of the Andromeda galaxy. Waryum was then Reassigned to Antarctica as X-K0940's handler on earth
  • The aforementioned drunk incident where Kirito get's drunk and does something with the girls, considering the girls reactions (goofy smiles and blushes) It's clear what happened.
• No Social Skills: Kirito. His thinking anime is a good reference for social situations is one of the LEAST relevant examples.
• "Not So Different" Remark: PoH does this to Kirito, calling both of them monsters who hide behind smiling masks. Although it doesn't do much in the long run, it does bother Kirito considerably.
• Omake: Starting with Chapter 5 ^note Chapter 5: Hidden Nature, each chapter is followed by a series of omakes titled 'Lusus + Vampire' which is a Crossover with Rosario + Vampire
• One-Winged Angel: Disturbingly common given the nature of our protagonist and what he winds up doing to other people:
  • Kirito and Mirai, several times, when they're in a pitched battle, whether in the main story or the Omakes.
  • Some time after being turned into hybrids, all of the Sleeping Knights mutate into grotesque new forms which enable them to fight at full potential.
  • Kage-chan and her spawn after being converted into hybrids by Kirito.
  • Kirito's progressive mental breakdown culminates in his ascension into the Incarnation of Hate, with a genocidal agenda to match. Thankfully, he gets better.
  • In the epilogue, the entire human race.
• Organic Technology: How Tryum technology is described as.
• Really 700 Years Old: Kirito, while appearing the same age as his canon counterpart is in fact over 350 Earth years old according to Waryum.
• Reassigned to Antarctica: Essentially how Waryum ended up on Earth as discussed in Noodle Incident
• Sanity Slippage: Eiji's fall to villainy here is a result of this. First, he gets captured and tortured by Mirai, then he finds out Yuuna knew all about Kirito all along and loves him despite him being an alien. His willingness to become a lab rat for Kikuoka and becoming a Super-Soldier hasn't done his sanity any favors.
  • It is discussed a few times that the girls who accepted and honestly love Kirito even though he's an Eldritch Abomination are not quite right in the head anymore. This started out with just Suguha but eventually extends to Asuna and Yuuna as well, with the others still in the transitional process by the story's end. Of course, by then no one seen in the epilogue is human anymore.
• Shout-Out: When going to Akibahara for a gift for Suguha, Kirito decides on a figurine of a red-haired swordsman with a cross-shaped scar on his cheek.
  • When asking Moka about vampires, Kirito asks if they sparkle, Moka replies no and remarks to feel oddly insulted by it.
  • He apparently took lessons on making friends from the Second White Devil.
  • He and Inner Moka perform a Double Rider Kick on Gin.
• Stock Quotes: Some of the curious/sinister/hilarious Scene Break Quotes are these. Some are Tropes and others are just made up to fit the scene.
• Shapeshifter Baggage: Kirito's Natural form is the size of a 16-wheeler truck but he has no problem taking the shape of a normal human.
• Spared by the Adaptation: All the Sleeping Knights. See LEGO Genetics above.
  • And, due to SAO not being a death game, everyone who died playing SAO in canon (Not that we know what they were doing). Also, Kayaba doesn't become a virtual ghost.
• Token Evil Teammate: Believe it or not, PoH, of all people, is hired to help rescue Kirito from government capture. And in the epilogue, the entire Laughing Coffin guild.
• Wacky Marriage Proposal: Kirito, when he burst into a restaurant and dramatically proposes to Asuna in public. She accepts. Incidentally, this event kick-starts the harem into becoming a reality.
• What Could Possibly Go Wrong?: What Minetaka thought after resuming the drive home. Also, the following Scene Break Quote.
• Why Did It Have to Be Snakes?: Kirito is afraid of water. Ironic, in that it's confirmed he had been 'deployed' in fully aquatic planets before and that he should easily be able to adapt and survive even in the deepest parts of Earth's ocean.
• You Called Me "X"; It Must Be Serious: Argo is disbelieving of Kazuto's claims of being an alien during Chapter 5. Then, when he insists it's not a joke, he refers to her by her first name, something he's never done in all the time he's known her.
• You Can't Thwart Stage One: Inverted. Kirito stops the Death Game before it even starts. By Confronting Kayaba, and convincing him not to go through with it.

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