So you have a CoolSword, AnAxeToGrind, or another bladed or EnergyWeapon that is [[AbsurdlySharpBlade absurdly sharp]]. Sweet! Now nothing can stand in your way, not even [[RayEnforcedDoor Ray Enforced]] [[ElementalCrafting adamantium-mithril alloy]] bulkheads! ... except for another, equally sharp weapon made of the same material, magical enchantment, technology or by the same UltimateBlacksmith. Why? Well, maybe your LaserBlade's [[SomeKindOfForceField containment field]] is naturally blocked by your opponent's. Maybe they're both so impossibly sharp that the prospect of one cutting the other is like trying to make water wetter by splashing it with more water? Perhaps since both were ForgedByTheGods, their nature as {{Empathic Weapon}}s recognizes a sibling and refuses to harm it?

Whatever the case, neither weapon will scratch or dent, much less become a WreckedWeapon. Only a direct hit on the opponent will end the duel... which is also likely to kill them unless your ImplausibleFencingPowers are good enough to disarm them without, [[JustForPun y'know]], [[AnArmAndALeg "disarming"]] them.

Needless to say, a character who thinks they have a DiscOneNuke in the form of their sword will be very unpleasantly surprised when facing an opponent who can even the odds. They may even get crushed if they've let their skills get rusty by relying on weapon's power. Such duels tend to prove suitably epic.

A SubTrope of MutualDisadvantage, of the "mutual invulnerability" variety. Contrast TakesOneToKillOne, when ''only'' like can cut like.

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!Examples:

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[[folder: Anime and Manga ]]

* ''BattleAngelAlita: Last Order'' manga. Monomolecular wire can be stopped by a stick made out of monomolecular material.
* In ''BlackButler,'' the Death Scythes can cut through anything. Naturally, a Death Scythe can't cut through a Death Scythe.
* Beam sabers in ''Franchise/{{Gundam}}'' are made up of a superheated [[MinovskyPhysics Minovsky Particle]] plasma encased in [[SomeKindOfForceField I-fields]]. I-fields cannot block regular matter, so what allows beam sabers to cut through almost anything is the fact that hitting something with your saber is literally letting the plasma of the saber eat through whatever you're trying to cut. When two beam sabers make contact, the I-Fields from both swords are repelling the plasma of the other.
** Beam shields, introduced in the second Universal Century, rely on the same general principle, they're basically a beam saber elongated into a wide plane that can be used to block attacks. Incidentally, if enough force is applied to a beam shield (or enough concentrated pinpoint power in the case of the Variable Speed Beam Rifle), it's possible to collapse it and hit the target behind it.
* In ''{{Guyver}}'', [[VibroWeapon high frequency swords]] can't cut other high frequency swords, and when two high frequency weapons come into contact with each other, they make a deafening shriek.
* Played straight in ''Manga/ShamanKing'', in that only [[MagicAIsMagicA Oversoul]] weapons can beat other Oversoul weapons (and Oversoul armor), but subverted when you get a character savvy enough to straight-up break their opponent's weapon, dispelling the Oversoul immediately.
* In ''{{Naruto}}'', Sasuke can [[ShockAndAwe channel lightning through his sword]] to give it incredible cutting power as well as inflicting paralysis, but both effects are cancelled out when clashing with one of Killer Bee's sword also enhanced (albeit differently) by lightning.
* In ''OutlawStar,'' Gene's caster shells could be blocked by firing another caster shell into them.
** Also subverted towards the finale, as there are some rare caster shells that will have abilities that only activate when blocked by another caster shell.
* In ''SamuraiSeven,'' the [[AbsurdlySharpBlade daito]] that the Samurai use can cut through anything from wood to HumongousMecha...except other daito.
* Gourry's energy blade sword in ''{{Slayers}}'' is eventually tested against another weapon that was created by the same people. When the two energy blades meet, they ''shriek.''
** Not only did they shriek, but they actually began to fuse together, and the energy released began to open a door to another dimension, [[SealedEvilInACan wherein dwelt]] the god-killing [[EldritchAbomination Dark Star]].
* ''Manga/DansaiBunriNoCrimeEdge'': No matter how powerful the Killing Good is, it cannot destroy another killing good.

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[[folder: Film ]]

* The energy discs in ''Film/{{Tron}}'' and ''Film/TronLegacy'' can cut through programs like butter, but will rebound off each other harmlessly. [[spoiler:Except at the end of Tron and Sark's last duel, where Sark tries a standard disc-block to deflect Tron's attack, but Tron is so much more skilled that his own disc flies right through Sark's (and Sark's ''head'') as if the latter were wet tissue]].
* [[LaserSword Lightsabers]] in ''StarWars'' have this property, along with the ability to reflect blaster bolts. Only a small set of non-saber weapons can effectively parry them.
** According to [[StarWarsExpandedUniverse ancillary materials]], Sith lightsabers have properties that can occasionally cause the blade they are clashing with to deactivate. This explains why Obi-Wan's lightsaber flickered when he fought Vader in ANewHope.
** More ancillary materials give you [[GreenRocks the Barab ingot crystal]]. This crystal, when inserted into a saber, gives it the ability to occasionally flicker and pass through a blocking lightsaber without destroying it.
** The "reflect blaster bolts" property was touched upon in a novel, wherein an alien race was able to defeat Jedi because their blasters (permanently set to stun) had a different frequency. Lightsabers could be tuned to reflect these blaster bolts, but then they were rendered moot against regular blasters.
*** [[FridgeLogic It makes you wonder why don't blasters then use some kind of spread spectrum technique.]]
*** Actually the reason was because the alien blasters (known as [[http://starwars.wikia.com/wiki/Ssi-ruuvi_ion_paddle_beamer Ssi-ruuvi paddle beamers]]) used a unique form of energy that couldn't be duplicated by conventional blasters because of their...[[PoweredByAForsakenChild unusual energy source]]. In any event, a regular blaster set to stun could still be blocked by a lightsaber without needing to re-tune it.
** Also done in Star Wars [=RPG=] games (starting with VideoGame/KnightsOfTheOldRepublic); when eventually acquiring a lightsaber, the player will soon find that, rather than the InfinityPlusOneSword they may be expecting, it's essentially an upgraded, shiny sword that only chips away heath rather than a GameBreaker.
* In ''Film/X2XMenUnited'', Wolverine and Lady Deathstrike both have the adamantium claws/fingernails. Likewise, in the ''Wolverine'' movie, Wolverine faces Weapon XI, which has an adamantium [[KatanasAreJustBetter katana]].
** Also in ''Film/XMenOriginsWolverine'', William Stryker shoots Wolverine in the head with adamantium bullets (which is kinda justified, as a bullet, which is really fast, could have more impact than a blade). [[HealingFactor Doesn't kill him]], [[EasyAmnesia but it does give him amnesia]] -- presumably the shock of the impact gave him severe brain damage and his HealingFactor couldn't piece all his memories back together.
* In ''Film/KillBill'', the only thing that can withstand the cut of a [[KatanasAreJustBetter sword]] forged by [[TheUltimateBlacksmith Hattori Hanzo]]... is another one.

[[/folder]]

[[folder: Literature ]]

* Shardblades in ''Literature/TheStormlightArchive'' can cut through any non-living substance except other Blades and [[PoweredArmour Shardplate]] as easily as swinging them through the air (they pass straight through living flesh without leaving a mark, but kill the victim anyway). While Shardplate can only take a few hits from a Blade before shattering, the Blades can parry each other indefinitely without harm. [[spoiler: This is probably because a Shardblade is the physical manifestation of a [[ElementalEmbodiment spren]] (it's complicated), while the origin of the armor is yet unrevealed but presumably different.]]
* In the ''IncarnationsOfImmortality'' series, the highly magical Red Sword wielded by War cannot cut through Chrono's hourglass.
* In ''Literature/HarryPotter'', Harry's and Voldemort's wands behave quite strangely when they try dueling each other, due to the wands being "twins", having feathers of the same phoenix as their respective cores.
* Played with in MichaelMoorcock's ''[[TheElricSaga Melnibone]]'' series; early on, Elric, armed with the runeblade Stormbringer, faces his cousin Yyrkoon, armed with Stormbringer's "sister" Mournblade. True to the trope, Stormbringer--which can cut through just about anything else it comes across--can't do that to its twin blade, and the cousins have an old-fashioned swordfight. As the battle progresses, Elric slowly masters Stormbringer, which has a will of its own; conversely, Yyrkoon allows himself to fall under Mournblade's control, with the result that Stormbringer and Elric neatly overpower Yyrkoon and Mournblade... casting Mournblade into hell, or at least another plane. That part's never really explained clearly.
* The titular SwordOfTruth has been known to cut through any weapon or armor - except for one case when a similarly enchanted blade is encountered.
* Averted in SergeyLukyanenko's ''Literature/ALordFromPlanetEarth'' with the [[AbsurdlySharpBlade planar swords]]. While a planar (or [[SharpenedToASingleAtom monoatomic]]) sword cuts anything, it's similar to a [[StarWars lightsaber]] in this regard in that it passes through like knife through butter. When two planar swords meet, one will always cut through the other. Which one is determined by the angle of impact and the sharpness of each blade. This completely changes how people fights with these weapons. So no {{Blade Lock}}s here. Unlike lightsabers, anyone can use a planar sword given sufficient training, and you can get them anywhere, although they're only produced on one planet.

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[[folder: Tabletop RPG ]]

* ''TabletopGame/{{Shadowrun}}''. To stop monofilament attacks (e.g. a monofilament sword), wear armor/clothing with monofilament threads woven into it.
* Nicely averted in ''TabletopGame/{{Warhammer 40000}}'' where Power Swords and Monofilament swords will destroy each other if their edges cross. Both will nicely cut through a regular sword, too.
** Played straight in the case of power weapons contacting other power weapons. The disruptive fields surrounding such weapons clash but typically prevent any damage to the physical component of the weapon itself.

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[[folder: Video Games ]]

* In ''VideoGame/SwordOfTheStars'', Mesonic Torpedoes will [[ArmorPiercingAttack go through all]] DeflectorShields except for Meson Shields.
* In ''VideoGame/SuperRobotWarsOriginalGeneration'', one of the very few things that can stop Sanger Zonvolt's Colossal Blade is another Colossal Blade, wielded by his EvilTwin.
* Despite the utterly insane powers of the Red/Blue/[[spoiler:Gold]] Keys of ''VisualNovel/UminekoNoNakuKoroNi'' (including, but not limited to preemptively disallowing any sort of defensive concept) they can clash with each other. Note that in [[AllThereInTheManual the Tips section]] it is mentioned that the Keys are [[{{Handwave}} limited in power for that Game Board]], presumably to stop Dlanor swinging her sword twice and ending the story instantly.
* Singular ''VideoGame/{{Minecraft}}'' example: Golden Pickaxes cannot mine Gold Ore - all other non-wooden pickaxes can mine the ore they're made of, but gold, true to RealLife, is exceptionally weak.

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[[folder: Western Animation ]]

* When ''WesternAnimation/SamuraiJack'' first meets the Scotsman, he's surprised to find his nigh-invulnerable sword cannot as much as scratch the Scott's similarly-enchanted weapon. The two spend the ''entire day'' fighting, and only succeed in exhausting themselves.
** When asked what made his sword special, the Scotsman replied "magic runes, laddie". This implies that his claymore, like Jack's katana, is endowed with magical properties, by gods or otherwise.

[[/folder]]

[[folder: Real Life ]]

* Averted, strangely, in the case of diamonds. [[http://en.wikipedia.org/wiki/Diamond_cutting#Bruting Bruting]] is a process wherein two diamonds are used to cut each other to desired shapes.
* Magnets: The sides with the same polarity will always repel each other.
** Unless brought together by a greater force. Then colliding into each other both chips chunks off (reducing the magnetic power), and reduces the magnetic power further through the interaction of their respective fields.
** This occurs in the sun. Stars basically start off as a collection of high energy protons, which collide with each other to create energy. The problem is, all protons are positive, and therefore, repel. The sun simply isn't hot enough to give the protons enough energy to overcome this propulsion, making it a seeming impossibility under classical physics. Quantum physics shows that protons could 'tunnel' through the repulsive effects of electromagnetism and collide with another proton often enough for fusion to work.
*** Even more basic, the nucleus of an atom shouldn't be able to exist if the universe only had the Electromagnetic and Gravitational forces, considering it's basically a dense cluster of protons and neutrons (which add nothing). One of the four fundamental forces of nature, the strong force, keeps them that way.

[[/folder]]
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