It's common knowledge that blades are cool. But they can also be a hassle to carry around everywhere. The scabbard might be uncomfortable, and the sword won't simply stick to your back. On top of that, once you finally decide to unsheathe your weapon, you are no longer able to hold anything else in one or both of your hands (or makerudegestures to your opponent). This problem is intensified if the weapon user intends to dual-wield.
The solution: attach the blade to your arm, leaving your hands free to do whatever else you may be inclined to do with them. These blades are often long, vaguely triangular, and taper to a point.
Variants include attaching the blades to your elbow, wrist, or even the back of your hand. Robots, cyborgs, and other non-regular human characters often take this one step further, embedding the blades inside their arms, from where they can be deployed and retractedby thought alone. At the farthest end of the spectrum are characters who replace one or both of their hands or even their arms with large swords. This version is Awesome but Impractical, as the blades prevent their wielders from performing mundane tasks when not in combat. They are also especially prone to Fake Arm Disarms, as they can be destroyed without gravely injuring the characters. While these drawbacks mitigate many of the practical benefits of having swords attached to your body as opposed to carried, few will have the guts to question your coolness or badassery.
Wolverine Claws are a specific variant. May overlap with Swiss Army Appendage. Can be considered a subtrope of Cool Sword. Compare its counterpart Arm Cannon, as well as Power Fist. Not to be confused with Shapeshifter Weapons, which are not limited to simply being blades. See also Hook Hand. Compare Combat Haircomb.
The examples below are divided into three categories: one, where a blade attached to the arm is a weapon of choice, but not a permanent body part; two, where the blade is permanently attached to the arm and may or may not be concealable; and three, where the entire arm is a blade.
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First kind (removable arm blade):
Anime and Manga
Angel from Angel Beats! has five of these as her first Guard Skill.
In D.Gray-Man, the Inspector keeps a switch-blade sword hidden up his sleeve.
Jintetsu is equipped with a knife in his mechanical elbow. For some reason, he rarely uses it after the first volume.
A villain in Blade of the Immortal, when he loses his sword hand to the titular hero, carves off the continuously rotting flesh of the stump and reinforces and sharpens the bones to use as a weapon. (And later on he does the same with his other arm.)
Sora of .Hack//Sign, who has one on each arm. His are retractable and theoretically removable, but he never takes them off. In the .hack// games, Kite can also attain this type of weapon (even specifically named after Sora), though it's not his only one.
In the anime, the Robot Girl Chachamaru from Mahou Sensei Negima! gets a long, thin, retractable sword installed in her forearm, in addition to steel angel wings. In the manga, however, she gets a massive sword that replaces her arm entirely. The other arm turns into an equally huge machine gun.
Veronica in Franken Fran appears to be stuffed with spring-loaded weaponry. Given her Artificial Human nature, she may very well be literally full of weapons.
Tengen Toppa Gurren Lagann does this with drills: the Gurren Lagann's usual weapon is a pair of drills coming out from above the wrist so in a sense it's also a Power Fist. Justified in that the Gurren Lagann can spawn drills from any part of it's body.
Sango from Inuyasha has a hidden retractable blade in her right sleeve that she uses as a last resort.
The ninja Hanzo in Hunter X Hunter has a retractable version. He uses it to threaten Gon during their fight in the final Hunter Exam.
Edward Elric of Fullmetal Alchemist often uses alchemy to transmute his automail right arm into one of these blades, built in blades are also common for others with automail.
Gundam 00 has the Gundam Exia, whose main weapon is a combinationbeam rifle and solid sword mounted on its right arm. Near the end of the series, its upgrade the 00 Gundam gets an improved version.
In X-Factor, sword wielding Shatterstar made a reappearance after a lengthy stay in Comic Book Limbo, sporting an updated look in an attempt to drag him out of the Dark Age. This new costume includes a leather jacket which covers a mechanism that houses blades on either side of his forearms. So he's actually got FOUR of these.
Étienne Cazenac, the protagonist of the French comic La Croix de Cazenac, fights with knives (or, in one arc, shards of bone) tied to his wrists.
Christian Szell, the White Angel of Auschwitz from Marathon Man, wears a spring-loaded blade in his sleeve to dispatch any concentration camp survivors who might recognize him. The film illustrates the main drawback of the Blade Below the Shoulder when Szell impales himself while tumbling downing the stairs.
Karl Ruprecht Kroenen in the film version of Hellboy.
Concept art for Star WarsEpisode III featured a lightsaber gauntlet, with two blades attached to the user's forearms. The idea was eventually realized in toy form in The Clone Wars line.
In A Nightmare on Elm Street Freddy Kreuger's blade-fingered glove started out this way, when he was still alive and his glove, merely a homemade murder weapon. In dreams, it evolves into more of a built-in weapon, which alternately appears on his hand whole when he sheds a disguise, or sends its blades springing out from his (or a puppet's, or a possessed boy's, etc) fingertips. In Wes Craven's New Nightmare, a scene is filmed in which Freddy amputates his hand and replaces it with a razor-tipped robotic version, but this element doesn't seem to have carried over into the character's subsequent appearances. See also Wolverine Claws.
Undercover Brother. During the final battle with Undercover Brother, Mr. Feather reveals short retractable blade claws that extend from below his sleeves.
The Predators have retractable wrist blades that extend to a punching, slashing length. In some versions they become very long arm swords almost.
Overlaps with the second category: the blades are retractable but are permanently attached. Removing them is fatal to the wielder.
Abigail in Blade Trinity has a small silver blade that springs from her wrist that she often uses for killing blows
At the end of Enter the Dragon, Han uses a Katara like weapon against Bruce Lee.
In Stephen R. Boyett's novel Architect of Sleep, the soldier caste of the raccoon-like sapients wear a 'Fighting Hand', a bracer with a hinged plate that folds down to cover the back of the hand with a palm strap to keep it in place; the hinged plate has four daggerlike blades usable in close combat.
Inigo Skimmer in the Discworld novel The Fifth Elephant had a blade cleverly concealed along his forearm(s), as well as a sharpened metal edge in his hat, and blades on his boots.
He also might be the only character in the series shown to have any competence with wrist knives. In Night Watch, Vimes remarks that even most Assassins think they're stupid and ineffective weapons.
Inigo's blade is pretty much the Assassin's Hidden Blade, which is extra funny because a) he is an actual Discworld Assassin and b) The Fifth Elephant precedes Assassin's Creed by several years.
In Hannibal, Dr. Lecter arms himself with a spring-mounted concealed blade known as a Harpy. Available at any gun and knife show, apparently.
It is, in fact, a SpyderCo Harpy. The spring-mounted bit is all Hollywood, though.
Sten of the Sten series has a special knife sheath surgically implanted into his arm so he can carry a concealed blade at all times.
Scythe-arms in Chronicles of the Kencyrath by PC Hodgell are blade pairs attached to the fore-arm, with the longer blade jutting forward and the other back. They are used in pairs, ie one main blade and one spur on each forearm. Training with them easily dissolves into chaos, with inexperienced users not being able to keep track of the spurs. Jame, the protagonist, is an exception, finding in them for the first time a weapon that she feels right with; she subsequently carries them everywhere.
The Gutbuster Brigade in R. A. Salvatore's The Legend of Drizzt series. They wear bladed/spiked armor on which they regularly impale opponents, in addition to carrying massive axes or hammers. Their leader has been known to walk around with an entire hobgoblin impaled on his helmet, and to kill orcs by running into them chest-first and thrashing violently until the orc stops screaming.
In the miniseries The Stand, Dayna Jurgens tries to use a retractable blade tied to her arm and hidden in the sleeve of her nightgown against Flagg. He turns it into a banana.
As seen in his self-titled spinoff, Angel has a set of retractable stakes that can pop out of his sleeves. Not blades, but just as effective, as evidenced by the piles of dust that used to be vampires. In the same series, Wesley uses a folding sword that pops out of his sleeve. He appears to hold it like a normal sword once its extended, though. When he loses his memory in one episode the practical problems of the concept are lampshaded, i.e. he nearly kills himself. And at one point, Connor shows up with an axe blade strapped to his arm.
In at least one episode they're using forearm-mounted crossbows!
Angel's retractable stakes became iconic for the series, remaining in the title sequence until the final season, and reappearing one last time (used by Gunn this time) in the Grand Finale.
Apophis uses one in Stargate SG-1 in an attempt to kill Sokar. Though he failed, it's amazing he even got close enough to try, as said blade was a huge and very obvious device on his arm. He does manage to take out Sokar's First Prime and a Jaffa guard with it, though.
Jean Renault in Twin Peaks. He uses it to kill a random strawberry and Blackie, the madam of One Eyed Jacks.
The Stinger Blade wielded by the Blue Stinger Beetleborg is one of these.
In Power Rangers Jungle Fury, Dominic the White Rhino Ranger's morpher is this, able to be summoned from a bracelet. The blade's handle is gripped in a fist-like fashion similar to a sword; however, the blade is aligned with the user's arm rather than being perpendicular. Known as the Rhino Blade, Dominic's weapon can also loose a powerful Super Slash finishing attack and also houses an alternate laser cannon mode.
Merle Dixon on The Walking Dead has an interesting variant of this trope where the bayonet attaches to a prosthetic arm he wears over his right stump.
In 4th Edition, any sort of one-handed weapon can be attached to a Warforged's arm. However, they function like type three model in that the Warforged can't actually do anything with that hand while the weapon is grafted onto it, although it can be removed voluntarily and fairly quickly.
Actually, light weapons can retract into the Warforged's arm, if made with a specific type of attachment.
Not just fourth edition, they could do it in 3.5 as well. All the rules were a bit byzantine.
Quite the opposite problem, actually. No rules were given on how to make an item as an attached or embedded component, other than "you can."
Shadowrun gives us Forearm Snap-blades, which functions as an alternative to the more famous Spurs. These are meant for the runner who either doesn't have the cash for or doesn't want to deal with the Essence loss imposed by cyberware.
The Melee weapon in Star Wars: Republic Commando is a miniature vibroblade mounted into the back of a clone commando's gauntlet. Crosses over slightly with type 2 because the blade is a part of the armor. It's very effective.
In Advent Rising, the Aurelians have large, scythe-like blades attached just below the elbow - and pointing backwards. Their fighting style consists primarily of elbow jabs.
In Assassin's Creed I, Altaïr's Hidden Blade. Note that to make this blade usable, the ring finger of Altaïr's left hand is cut off. His sequel successor (and descendant) Ezio on the other hand seems to have pulled this off (on both hands, even) without the nasty "cutting off fingers" catch.
In game this is justified by having the base of Ezio's blade (inherited from his father) modified so it's raised further from the wrist, compared to the original design in Altaïr's day. This was actually Altaïr's idea — the first "Codex" page that's decrypted is his design for this blade, which another page implies that it's because hiding in plain sight ("social" stealth) is difficult with a missing ring finger — but Leonardo da Vinci would implicitly take credit for it. It doesn't stop him, however, from taking a moment to freak Ezio out by pinning his hand and raising a meat cleaver before saying "Just kidding."
In Brotherhood the Prowler — a Templar attempt at fighting Assassins using their own methods — also has a forearm-mounted switchblade, if a wider and less fine-looking one, whose two blades pivot at the back to form a single blade in front. Ezio had to abandon the second (built by Leonardo, right-handed) of his Hidden Blades at the Siege of Monteriggioni, but had the original left-handed one replaced (or covered with a single-piece metal vambrace) upon his arrival in Rome, and Leonardo later constructed for him another right-handed Hidden Blade that now fit into the wrist of a leather glove.
And in Revelations, Ezio loses his right-handed hidden blade again (the intro video shows him losing his left-handed hidden blade, but in gameplay he's missing the right-handed one) and has it replaced with one modified by the Assassins in Constantinople to have a hook on the end of the blade, allowing for more maneuverability when climbing and new abilities in combat.
Each of Ezio's recruits in Rome was issued a Hidden Blade created by Leonardo da Vinci (as revealed in the Facebook game Project Legacy). By 2000 it had become "mostly ceremonial," but was still in use by the Assassins, and in fact Desmond Miles fought off a Templar invasion of an Assassin safehouse by wielding one.
Governor Tekagi from Freelancer also has one of these.
In Halo: Reach the Elites are issued with a wristblade, close to the Energy Sword. Gameplay-wise, it only appears during assassinations, since it's supposed to be the Elite equivalent of the Spartan's combat knife.
Street Fighter EX's Doctrine Dark wields a pair of retractable katars on the edges of his forearms that pop out below his wrists. Said blades have various lengths depending on D. Dark's special move/super combo.
The Protoss Zealots in Starcraft have Energy Blades mounted in their armor. Dark Templar wield a single Warp Blade on their right wrist.
The Sai faction in the game Stormrise have access to the Spectre unit type that fights with energy blades projected from it's forearms.
With Weapons Customization, Arm Blades are offered in City of Heroes for the Claws powerset.
Chipp Zanuff of Guilty Gear has an odd variant. His weapon is a blade that runs parallel to his forearm and is attached to a armband he wears there. In the opening animation, he sometimes clicks it into place
The Garo in The Legend of Zelda: Majora's Mask have a scimitar strapped to each hand. Although they could be holding it under their ponchos, the attacks they use suggest otherwise.
In the Overlord series green minions will convert weapons they pick up into blades attached to the backs of their hands (starting with two blades on only the right hand with very basic equipment, like farming tools and ending with three blades on each hand with the most powerful equipment).
Rayne in the BloodRayne games wears sword-length blades attached to wrist cuffs; they mechanically rotate and extend in the same direction as her lower arms, with grips that she holds to keep them in place.
Let's not forget Voldo, that nutcase. His weapons include wrist-mounted motorized meat grinders, guillotine blades, pairs of antlers and regular katars.
Dampierre's twin hidden daggers in Soul Calibur: Broken Destiny and also SoulCalibur V.
World of Warcraft features "Fist Weapons" that can range from things that look like brass knuckles to full-arm sleeves featuring teeth, claws, spinning blades and/or other accessories.
Big Sisters from BioShock 2 have a massive hypodermic needle which they use to impale enemies.
In the Dark Storm mod for Cortex Command the Tengu armor guys use an electro-magnetic charged knife which is attached to their wrists (like the Assassin Blade in one of the above examples)in their melee attack, the knife was once a separate weapon in the mod up until lua's introduction in the game.
Elites in Halo: Reach and the Arbiter at the time of Halo Wars both carry retractable Energy Swords in the armor on their wrists. Reach's Elites have small blades that only appear in assassinations while the Arbiter carries full-length swords on both arms.
Kiros in Final Fantasy VIII uses a pair of katar (mistranslated in the English-language version as "katal").
Mass Effect 3 brings us Omni-blades, diamond-hard searing hot blades flash-forged by one's omni-tool.
Alex Mercer can change his arm into a giant blade from the shoulder down on command. It is sharp enough to slice through the toughest hides and metals including tanks at the cost of having to kill and consume hundreds of people to stay alive.
James Heller and all the other Evolved that Mercer created in the second game also have this ability, more so with the other Evolved who, unlike Heller, seem to have just one special ability and dual armblades from the shoulder down.
Sundowner, a cyborg boss from Metal Gear Rising: Revengeance fights with a pair of machetes, one of which he attaches to a hinged clamp on his forearm while holding the other in his hand, which turns his entire arm into a makeshift scissor with enough strength to decapitate any unfortunate soul in between the blades.
Coheed of the The Amory Wars has several curved blades along his left forearm.
Kor'Maril in Drowtales has these to compensate for his height.
Zeetha in Girl Genius uses a pair of swords with horizontal grips, similar to Katar (see below), which effectively extend over the tops of her hands.
Arminius Vambrey, a vampire hunter in Sluggy Freelance, conceals stakes in his sleeves. "And you thought these elbow pads just made me look tenured!"
Waterworks features an entire alien race where each person has four long blades affixed to their legs and arms since birth, useful for all kinds of things. They're a major part of the culture, and losing one's blades or not caring for them properly is grounds for social stigma.
A minor villain in Batman Beyond had retractable chainsaws in his wrists and knees. The latter proved to be a liability as they got stuck on walls and floors.
The wielder still has to hold both katar and pata. They're not attached to the arm; they're just held with a grip perpendicular rather than axial to the blade. That being said, they are almost certainly the inspiration for this kind of weapon in fiction.
In reality, a blade like this would be impractical, both because the wrist joint is so important in the use of a sword and because it would be dangerous to the user. A hard blow to the blade could potentially cause the forearm to break.
You could use it to stab people effectively, but no one ever seems to do that.
Strap-on climbing spikes are sometimes used by professional tree trimmers or phone linemen to climb tree trunks and telephone poles. Subverted in that they're strapped to the legs, not the arms.
Second kind (permanently-attached blade):
Anime and Manga
Jeremiah Gottwald from Code Geass (pictured above). After having his body effectively rebuilt for the second time, he gains two concealed swords, one in each arm.
As you can see from the picture, his blades are longer than his forearms. Given that the movement of his arms is in no way impaired with the blades retracted, and the blades clearly are not telescoping, it's unclear how this actually works.
Taopaipai from Dragon Ball is rebuilt as a cyborg with this type of blade. He reveals it in his fight with Tenshinhan, using it to inflict the wounds that later become Tenshinhan's chest scars.
The Guyver suit has two lethal blades attached to the forearms just in front of the elbows.
Gally/Alita from Gunnm had elbow blades during her Motorball days, and although they later got mounted on a blade for a time, Gally later recovered them in their implanted form with her Imaginos body.
Mazinger Z: In the last season, Mazinger-Z got equipped with the "Iron Cutter", two retractable blades stored in each arm. Often he used them in combination with its Rocket Punch to slice enemies from far.
UFO Robo Grendizer: Each fist of the titular mecha was surrounded by triangular blades pointed backwards. When Grendizer used its Rocket Punch, those blades bent forward. So, the enemy was shredded being being punched.
In Katekyo Hitman Reborn!, Varia officer Squalo has an artificial hand with a sword attached to it. The hand can be flipped to cover blind spots.
Witchblade or Cloneblade users from Witchblade have extendable/retractable blades attached to their arms. The main character, Masane, has one, while those with upgraded Cloneblades have two. Masane acquires another one after learning to increase her power using the Witchblade
Sasori from Naruto. He stuck his sword into Sakura's gut. Sakura planned on keeping him focused on her by holding onto the blade, thinking he wouldn't let go and would worry on just finishing her off first; But he then detached his puppet limb to reveal a blade within it where he promptly ran after Chiyo to finish her off next Didn't work out too well, he got stabbed right in the heart capsule by the first two puppets he ever created, the ones made in the likeness of his deceased Mother and Father. Then he died.
And X-23 by virtue of being his clone (she has two in each arm and one in each foot). And Daken by virtue of being his son (he has three on each arm, but one of them juts out through the front of his wrist).
In The Other,Spider-Man's body underwent a funky metamorphosis which primarily manifested in the ability to pop out "stingers" from his forearms. Because... y'know... he wasn't special enough, and giving him a pair of Wolverine-ripoff blades totally made him more unique. Fortunately, virtually everybody in existence has chosen to forget this little development since then.
In the opening of the Hellboy feature movie that takes place in WWII, Kroenen first empties his sidearm on the Allied soldiers before he has arm blades pop out his sleeves, and begins to slice and dice the unfortunate GI's. Near the end, he retracts the blades back into his sleeves when forced to perform a different action.
Weapon XI in the film X-Men Origins: Wolverine has full length retractable katana blades in each arm. At least Wolverine's blades might've slid into his forearm allowing him to bend his wrist. This guy has no excuse. The blades are in fact so long that he shouldn't even be able to bend his elbow.
Sabretooth in the same film has Wolverine Claws, what with him being Wolverine's brother. They grow out of his fingernails and are shorter than Wolverine's, but clearly operate on the same principle.
In Spider-Man 2, a stabbing blade is concealed within at least one of Doctor Octopus's Combat Tentacles, which appears from the centre of the claws when deployed. What purpose such blades had in conducting research on nuclear fusion is anyone's guess.
Well, it could have been added in after the fact, when he decided he had to do whatever it took to do what he set out to do.
William Gibson's recurring razorgirl Molly Millions (from Neuromancer and Johnny Mnemonic) has retractable scalpel blades implanted in her fingertips.
One of the Ravenor novels has a throw-away character whose body has been heavily modified, with a blade like this being one of the additions. The character's hand split open, with the fingers forming a sort of grotesque guard, with the blade emerging from there. If that sounds like Squick then you really don't want to know what the new recurring character the scene introduced did to him.
The Hork-Bajir in Animorphs are basically walking Cusinart, born with blades attached to their elbows, wrists, ankles, knees, tail and forehead (the poor mother...). Somewhat anticlimactically, they use them for gardening and harvesting bark from trees.
Until some other aliens show up and parasitically possess them in order to turn them into a slave race of living superweapons.…
The Mantis-kinden in Shadows of the Apt often grow barbs down their forearms with their Art. They're most often used as a secondary weapon, though, adding one more way for them to kill you.
The Yevetha, the antagonists of the Black Fleet Crisis trilogy, have retractable blades in their wrists. Depending on the artist, it's either a single blade out of the inside of the wrist or two blades out the sides.
Model 0005 Cylons on Battlestar Galactica have retractable wrist-mounted blades for melee fighting. The newer Centurions instead have fingers that fold out into powerful claws.
In the "Look At The Princess" episode trilogy of Farscape, the Peacekeeper agent Jenavian Charto has a stiletto blade concealed in her wrist.
Mighty Morphin' Power Rangers: Rita's warzord Cyclopsis has twin wrist blades after being reconstructed by Lokar following the first time Ultrazord blew it up. It slices off one of the Megazord's arms and the drill tip of Dragonzord's tail. In Round 3, Dragonzord gets payback by using its tail to break the blades off.
The Celestial series battlemechs in Battletech usually mount a large retractable blade on one arm.
In Keith Baker's Dreaming Dark trilogy there is a Warforged named Indigo. She has two concealed blades in her arms.
Shadowrun offers hand razors, which are small blades implanted under the nails, hand blades, which extend along the outside of the palm and little finder, and spurs, which extend beyond the hand and can reach sword-like sizes. All self-respecting street samurai will have at least one implanted weapon.
In Warhammer 40,000, one piece of wargear available to Eldar are Power Blades, described as fitting onto the forearm and allowing the Eldar in question to wield other weapons in addition to the blades.
The company Macrotech advertises their version of this as "perfect when guns are illegal and swords are too inconvenient" in GURPS: Bio-Tech.
If we tried to mention all of the Bionic parts that granted this in Rifts, we'd be here all night. Not to mention the drills and chainsaws.
BattleTech has this in the form of Retractable Blades, which are giant metal blades fitted onto the side of a mech's arm for stabbing through armor at close range.
The Mortal Kombat character Baraka is a member of the nomadic mutant Tarkatan race, most of whom possess long retractable blades extending from their forearms. Baraka is not an exception.
Raziel of Legacy of Kain gets a wraith-blade bound with himself. It extends from his open hand on command.
At least until the last game, when it becomes a normal sword-shape. Boo.
The Pokémon Gallade is an odd variant. Ordinarily, his arms don't even have blades, but when he enters battle, he can extend his elbows to make them Absurdly Sharp Blades.
Given the shape of the arms in the game sprites, this could arguably be a combination of types 2 and 3.
Earlier in the franchise, we have Sceptile and its Leaf Blade.
Kunzite of Tales of Hearts has these as his prize for being the first playable robot in the Tales Series, and he gets the third kind as a bonus - two extra blades attached to flexible arms mounted on his back.
Humongous Mecha Soulgain from Super Robot Wars series has extendable blade on each forearms. Unextendable variant of said blades are used in Endless Frontier by combat android Cardia Basirissa and Arkgain, a smaller combat robot based on the Soulgain.
Serph from Digital Devil Saga, while in his demon form has two retractable blades protruding out of his forearms. At least they look to be part of his actual anatomy in that form.
Adam Jensen, the protagonist of Deus Ex: Human Revolution, has two straight, square-tipped blades hidden in his bionic arms, which can extend either from the wrists or elbows, allowing him to take down enemies in awesomely over-the-top ways.
Fulgore, a cyborg assassin in Killer Instinct, has plasma charged blades mounted on his forearms.
Bloody Roar: Xion the Unborn has these in his beast form. His Primal Fury ending cutscene indicates that they're either in his human arms too or he can at least access them without transforming.
Togera from War Of The Monsters extends spikes from its wrist during punch attacks, and Robo-47 replaces its hand with blades for some of its attacks.
The assassin Tinsnip in the Whateley Universe, who can manifest swords over both hands. Apparently, his 'signature move' is a scissors-snip. Squick.
In the third season premiere of Transformers Animated, a newly-upgraded Sari Sumdac has a pair of energy-blades extending from within her forearms, though they are later permanently disabled and never seen again.
Word of God (by which I mean Wyatt's formspring) is that they're still there, but their power output has been heavily reduced. Sari probably isn't too keen to use them again after what happened to Bumblebee.
Arcee from Transformers Prime has two forearm-mounted blades, while Ratchet has retractable ones that can replace his hands when necessary.
Optimus has the swords that debuted in the movies.
Mantids (such as the Praying Mantis) actually have two of these facing opposite directions that act as pincers when the arms are extended.
Third kind (blade replaces hand or arm):
Anime and Manga
Creed's Phantom Blade Lv.3 in Black Cat replaces his arm with a Tao Blade and sprouts an extra arm.
Eve in the same series usually morphs one of her hands into a blade to use as a Shapeshifter Weapon.
Shira in Blade of the Immortal, after losing a hand, decides to sharpen the bones in his arm and use that as a blade. Apparently, when he decided this he forgot to consider that it would hurt like hell to hit something with it. Like he'd care anyway...
Great Mazinger: Several [[Robeast]] has bladed weapons -or even spiked maces- instead of hands or arms. The first examples appeared in the last episode of Mazinger-Z (Gratonios) and in the first episode of the sequel.
The true form of Allen Walker's Innocence in D.Gray-Man is a BFS that is made from his arm. Different from the usual "third kind" of this trope in that the sword isn't attached to his body any more- he has to hold it in his remaining hand.
Snimon from Digimon is a virus-hunting praying mantis sniper (mind you, all of that besides "praying mantis" is All There in the Manual and never witnessed, but he is pretty Badass) who cleaves opponents with its giant blades, and is capable of shooting pink crescent beams from them with its Twin Sickles attack (known as Shadow Sickle in Japanese. There's a badder version called Ultimate Twin Sickles, which increases the number of energy blades fired.) He's also one of the rare Mons who can overpower Digimon of higher levels than he.
Omegamon/Omnimon's Transcendent Sword is technically this, since it comes out of his "hand" - which is composed of a WarGreymon skull/helmet instead of an actual hand with fingers. (Unlike Snimon, we don't have to worry about how he picks stuff up. This is a Fusion DanceSuper Mode saved for special occasions and only taken on under dire circumstances. In his? Their? default form of Agumon and Gabumon, they've got hands, though Agumon doesn't appear to have thumbs.)
Similarly, there's Duskmon. Like Omni/Omegamon, the blades are extended from his "hands" with are shaped like a pair of draconic skulls. Unlike Omnimon, he spends a great deal of time in this form, making one wonder how he held things other than "biting" them.
Shurimon has giant shurikens for hands and feet, and his limbs are actually coils and are extendable. Again, combat form.
In Fullmetal Alchemist example: One of the combat automail arms that Buccaneer uses over the course of the series, the "Crocodile", is this combined with a chainsaw.
Envy at one point turns its lower arm into a blade when fighting Ling.
In the original anime, Envy uses the same trick on Ed, except this time he/she kills him with it.
Hyakkimaru, the main character of Dororo has swords concealed in his prosthetic arms, which slide off just below the elbow when he needs the blades. After he regains his real arms, he switches to wielding the swords as normal.
Gray in Gunsmith Cats equips himself with a bladed prosthetic after Rally Vincent blows off his hand. He swaps the blade for a hook for everyday use. He can shoot the blade like a spear using a powerful spring built into the forearm.
In Genzo the wild girl Otsuru uses a rusty blade as prosthetic right hand. Later the main character Genzo build a better curved blade for her.
Gavrill from Franken Fran, unlike her sister Veronica (Mentioned in Type 1 above), doesn't have blades inside her body, but is able to transform her body into, among other things, said blades.
Marvel Comics minor villain Razorfist, as the name implies, has two foot blades replacing each hand. The difficulty of, for example, eating are frequently lampshaded; Razorfist shirks all responsibility onto others to care for him (and they do because oh crap he is a crazy muscular martial artist with freaking swords for hands). This Razorfist is actually the second or third, depending on how you count it - he originally shared the name with his brother, each having only one blade-hand. He's so used to them that, whenever someone decides to replace them for prosthetic hands, he gets completely lost on how to use them.
Razorsharp of The DCU team books Psyba-Rats and Blood Pack was a Playful Hacker (with Cracker tendencies) whose superpower was that her arms could morph into swords. In Psyba-Rats she mainly used them to climb walls and break into buildings (in a good cause, usually); in Blood Pack she was reluctantly put in a position where she'd have to use them in combat.
The Avengers villain The Grim Reaper has a scythe blade on his right hand. Originally it was a Type One "techno-scythe" supplied by the Tinkerer. Later his right hand got amputated and replaced by a magical scythe when he was empowered by the demon Lloigoroth.
Amokk, from Hyperkind, has his hands replaced with foot-long blades. In the second issue, he laments that he'll never play the guitar again, until he and the rest of the team discover that they can shapeshift back to their human forms.
In the made-for-TV movie adaptation of Moby-Dick (the one that stars Patrick Stewart as Captain Ahab), Ahab and crew meet up with another whaling ship, whose captain lost an arm to the white whale. He had it replaced with a harpoon.
Wild Wild West. When Jim West fights several of Mad Scientist Dr. Loveless's altered men inside the giant mechanical spider, one of them has extendable sword blades implanted in his arms instead of hands.
In the third part of Piers Anthony's Battle Circle Trilogy, Neq the Sword, the titular character has his hands cut off by bandits. The surgeon who he rescued at the same time agrees to replace his left hand with a simple prosthetic claw, and his right with a sword. Unfortunately, his bad temper, coupled with a sword permanently attached to his arm, wind up causing unnecessary deaths. He remedies this by welding a glockenspiel to the sword so that it would never kill again. !
In The Malazan Book of the Fallen, the K'Chain Che'Malle (Big intelligent lizard creatures) are bred for specific purposes, so the K'ell Hunters have big blades instead of claws or hands.
The Katana robot in One Must Fall has crescent-shaper blades instead of hands while the Shredder robot has claw-shaped cutters. In both cases the blades are monomolecular.
Warcraft: Kargath Bladefist, the leader of the Shattered Hand Orc clan, had a blade attached to his arm after he lost his hand. Replacing a limb with a blade became a popular rite of passage in his clan, hence the name Shattered Hand.
Starcraft: The recognizable Zerg Hydralisk has arms that end in huge scythe-blades that it cannot use in combat(although it does in cutscenes), because somebody was unable to incorporate meele and projectile attacks in one unit. However in Starcraft II it will be able to finally use those blades(however the attack is only cosmetically differnt from its normal attack).
Also Starcraft has the Ultralisk which has two giant Kaiser Blades on its head.
The enemy type in The Suffering which symbolises execution by decapitation not only has forearms replaced by blades, but the legs below the knees too. Don't ask how it manages to maintain balance when running.
In Quest for Camelot Ruber does this towards the end with Excalibur with a magic potion that combines objects.
Shiv, a supporting Static Shock villain, could replace his hands with nifty energy blades. If memory serves, this power was relatively versatile, but true to his name, he always came back to this...
Optimus Prime again, this time in Transformers Generation 1, with an Energon axe in the three-part Series Premiere. Megatron had an Energon Mace. Despite using these weapons only that one time in the entire series, they're considered iconic to the characters, and even referenced by similar weapons in the movie listed above. Both of the characters Masterpiece series toys included plastic versions of the weapons. These were more of a combination of the second and third types, given that they retracted their hands to deploy them.
Yet another Optimus: his Transformers Prime incarnation has two arm-blades and two arm-cannons. Both of Ratchet's arms can also become short swords ("I recommend dissection.")
Not quite a blade, but a man named Aron Ralston who, after getting his arm trapped under a boulder for 5 days whilst mountain climbing, cut off his own arm to free himself, then proceeded to replace the amputated limb with an ice pick and climb the crap out of some more mountains. Chuck Norris himself would avoid this guy.
Galvarino, war leader of the Mapuche tribe in the 16th century, was captured by the Spanish and had both his hands cut off to serve as a visual warning to the rest of his tribe. Because he was a total badass, however, he went back to the tribe, got them super-pissed at the Spanish, and then tied blades to his arms to compensate for the fact that he had no hands. He then proceeded to lead an army against the bastards who disfigured him. The Spanish ended up killing him eventually (they wanted to let him go because they felt sorry for him, but he would hear none of it), but it's important to note that the Mapuche tribe was one of the few that never fell under Spanish rule (it joined Chile in the 18th century).