A hot blade is an edged weapon that somehow heats up, adding the thermal energy of its temperature to the kinetic energy of its blow to achieve Absurd Cutting Power. When active, it will usually glow visibly (without losing any of its structural integrity, somehow explanation ) because Power Glows. Compare Vibroweapon, which uses extremely rapid vibrations instead of heat to enhance its cutting power. A more advanced weapon is the Laser Blade, where the blade is made of Pure Energy instead of just adding (heat) energy to a physical blade. Hot blades are more common in a Science Fiction setting. Its more fantasy-oriented counterpart is the Flaming Sword; a hot blade retains a touch of Playing with Fire while requiring less Willing Suspension of Disbelief. Usually used with swords, but other bladed weapons are also seen occasionally. A subtrope of Absurd Cutting Power. Unrelated to the idiom "like a hot knife through butter"... though hot blades may, indeed, cut through things in such a manner.
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- In the Gundam franchise, the next step down from Energy Weapons like beam sabers is heat weapons, the most iconic of which is the Zaku II's heat hawk. Another well-known example is Gundam Sandrock's heat shotels, which become ludicrously huge in Endless Waltz.
- At one point in the original series, a heat hawk is able to briefly parry the Gundam's beam saber, which is formed from superheated plasma. You think its because a heat hawk blade would by necessity have a higher melting point than the Zaku's armor before you know that the All There in the Manual tells you the blade of the heat weapon is actually plasmarized and maintained its form (thus they are just lesser example of beam weapons with lower tech).
- In the battle at the sea in Berserk, Schierke's fire magic was used to turn Guts' Dragonslayer into one of these.
- In One Piece Enel does a variation by using his electric powers to turn his trident into molten metal in order to burn Luffy, who's immune to direct attack by Enel's lightning.
- Yaiba has Gold, who can apparently heat up his gargantuan Sinister Scimitar somehow. However he does this once.
- In Kuromukuro, Kennosuke, a samurai from the Sengoku Jidai, has a laser-edged katana that he took from an ogre. Recreated (sans laser) by Man At Arms.
- City Of Chains has Everburn, Lucien's two-handed sword. Despite the name, it is this and not a Flaming Sword.
- Tech 10 Rebooted has the Pyronaut Blade, an alien weapon that can pierce through most armor when at full temperature.
- XCOM: RWBY Within has Blake carrying a knife with a low-power laser in the handle, which heats the blade and allows it to more effectively penetrate armor and hardened skin. note
- Optimus Prime from the Transformers movies uses some of these to cut Decepticon's heads clean off.
- In Pirates of the Caribbean: The Curse of the Black Pearl, after Will uses his sword to jam the door of the smithy and cut off Jack's escape route, he grabs a replacement out of the forge. It looks impressively glowy but doesn't last very long; fortunately there are plenty more on the racks.
- The Hitchhiker's Guide to the Galaxy has a throwaway gag about a knife that toasts bread while slicing it.
- In The Wolverine The Silver Samurai was able to cut Wolverine's admantium-coated claws with a superheated Adamantium sword. Since Adamantium suffers from a Like Cannot Cut Like rule, presumably the intense heat melts the claws off.
- The Warpsword of Khaine from Malus Darkblade is said to feel like it just came out of the forge, and it burns whatever it hits.
- In Codex Alera many of the High Lords firecraft their swords, because a bleeding wound can be watercrafted better easily enough, but a cauterized wound is unhealable. Since this causes their swords to shine brightly, they also use them to send signals and challenges that can be seen across the chaos of a battle.
- In Clay and Susan Griffith's Vampire Empire series, it is Twenty Minutes In The Future and remnants of a steampunk British Empire barely escaped a vampire apocalypse. Among the weapons used by humans against the vampires is the Fahrenheit Blade. These are blade weapons, including khukris, that have a special sheathe which will coat the steel blade in volatile chemicals. This heats the blade to extremely high temperatures and are more devastating against the heat-sensitive vampires than regular swords.
- In Supergirl, Vartox wields a red hot axe that can cut a Kryptonian. Ironically, Supergirl destroys it by blasting it with heat vision until it can't take the strain and explodes.
- Many Warhammer swords (at least in the way they are visually depicted), both Warhammer Fantasy (Archaon) and Warhammer 40,000 (THE GOD-EMPEROR OF MANKIND), even when some flames might flicker depending on the artist, verging into Flaming Sword territory.
- Mutant Chronicles.
- Call of Cthulhu supplement Cthulhu Companion, adventure "Valley of the Four Shrines". The East shrine is dedicated to Cthugha, a deity made of fire. A sword found in a secret room can be made to glow yellow-hot, which will do damage to creatures vulnerable to fire.
- Exalted: A Malfeas charm turns a blade too burning hot to be wielded, forcing your enemy to either drop it or suffer lethal damage. Another version of this charm targets armor instead... and it's not easy taking off your armor during a (heh) heated battle.
- And of course Dungeons & Dragons is full of these. As well as (among others) lightning and cold versions. Not restricted to bladed weapons, though...
- 1001 Science Fiction Weapons for D20, by Plain Brown Wrapper Games, also has a section on superheated blades. Various blades are used, including a scythe; though unlike the supercooled weapons available in the book, the superheated scythe is not useful for non-combat reaping of wheat as the crop is set on fire. It is stated that if you see one of these hanging on the wall, you're probably dealing with a villain.
- In Obsidian - Age of Judgement from Apophis Consortium, one of the expansion books has a gun version of this trope. Normally flamethrowers are the weapons of choice against the undead, unfortunately they come in only one size and don't do that much damage compared to the larger machine guns. So a new weapon was invented, it's a gun with a mechanism that separates the bullet from the casing. It then superheats the bullet until it's almost molten and then the casing with charge is fired. So the super-hot bullet is shot out at high velocity and will rip up standard targets, while also incinerating enemies that are bullet-resistant.
- The Heated Cosmic Knife from the Dead Money expansion of Fallout: New Vegas is this. It's an indestructible Absurdly Sharp Blade that has been heated with a heating pad and apparently retains its heat for a ridiculous amount of time, giving it even more destroying power.
- There is also the Saturnite Fist in Old World Blues dlc. Just give it to the crazy toaster in Big MT and it will become the Saturnite Fist Superheated which glows red hot and sets enemies on fire. A wonder how you don't burn your own hand while wearing it.
- One of the bosses from Chrono Cross uses a Steampunk version (a Nigh Invulnerable, Humongous Mecha), but this is technically a fantasy setting.
- The (in)famous Pyrotechnic Axes in Arcanum: Of Steamworks & Magick Obscura presumably work this way. They're one of the strongest weapons in the game, assuming you're a melee-based technologist.
- Strider Hiryu's Cypher uses plasma to achieve this effect.
- Nero's Red Queen from Devil May Cry 4 has a special mechanism inside it; the sword has a gasoline fuel inside, and the sword can be revved; when doing so, it sprays out the fuel to the blade as well as igniting it, making the blade glow hot red.
- Though they are not technically swords, the hooks thrown by Spider Splicers in the BioShock games are glowing red hot. They are probably heated by plasmid use on the part of the splicers.
- The Thermic Lances in X-COM: Terror from the Deep are a combination of Hot Blade and Vibroweapon, and are pretty effective against the Demonic Crabs. note
- The final upgraded blades for the Rangers in XCOM 2 are hot enough to set enemies alight sometimes.
- The Omni-blade in Mass Effect 3, the hologram is so the user doesn't accidentally burn themself.
- In Metal Gear Rising: Revengeance, LQ-84-series UGs can throw superheated knives that are able to penetrate (and partially melt) stone and metal. Perhaps notably, Sam's sword also has a distinct red blade but isn't a Hot Blade; just an exceptional Vibro Weapon. Sundowner's weapon also seems to count, as visible heat and steam can be seen as he slowly slices across the President's neck in the intro
- A variation from Half-Life 2: an electromechanical crossbow that launches red-hot rebar rods.
- Warframe has the Heat Sword, Heat Dagger, and Dual Heat Sword (sword+dagger combo), which do fire damage on some of their special attacks. All of them have visibly red-orange blades with glowing segments. Grineer melee weapons like the Cleaver, Machete and Sheev also have red-hot powered blades.
- In Super Robot Wars Compact 2, the Alt Eisen carries a "Heat Horn" mounted on its head and functions like the Heat Hawk of the Zaku II. When it's rebuilt and upgraded into the Alt Eisen Riese, the weapon is turned into the "Plasma Horn", with an additional feature of Shock and Awe.
- Sol Badguy's Fireseal(and it's upgrade, Junkyard Dog) allows him to channel his flame powers better. It also allows him to cut with it, despite the blade part being a blunt rectangle.
- Sparkster the Rocket Knight sheathes his sword in his jetpack, and several of his stronger attacks have his sword glowing with a blue, orange, or red flare indicating that he traps the heat in his sword. One of the powerups he can find in RKA 2 upgrades him outright to a Flaming Sword.
- In Yandere Simulator, Yandere-chan has the option to heat up a knife blade with blowtorches. As of right now the effect is more cosmetic than of practical use...unless you want to turn it into a Flaming Sword instead.
- Sufi tortures a 16-year-old boy with hot knives in order to "exorcise" him.
- Heated blades have been used for crude amputations to cauterize and disinfect the wound.
- Actually not a good idea in real life, even if it were feasible; as any blacksmith or metalworker can attest, steel loses its hardness the closer it gets to its melting point. It'd take some very special metallurgy for the material to both glow white-hot and still be viable as a hard cutting edge.
- Such special metallurgy has existed since the 1930s or so with "high speed steels" - which were developed in response to modern industrialized machinery (like drills, end mills, ect.) becoming more capable and having higher RP Ms. So, instead of finding roundabout solutions to the problem of drill bits heating up and dulling because of it, high speed steels were developed which simply retain their regular hardness at high temperatures with addition of molybdenum, tungsten and cobalt. With some of these steel alloys, operating temperatures in excess of 500°C (almost a thousand degrees Fahrenheit) are possible. More if you're willing to sacrifice some hardness. To make things even better for potential application of this, high-speed steels are popular in high-end cutlery and knife making. Steels like CPM M4 are becoming extremely popular because of how "hard" the steel can be ran (usually well above 60 HRC, which is about where most steels start to top out at before becoming too brittle - some alloys can almost reach 70 HRC, which is nearly on par with the higher end of ZDP-189) and it's wear resistance. Steels like CPM M4 and CPM Rex T15, especially, on a properly forged knife would seem like space voodoo magic to someone unaware that such capabilities were possible. Heating one up, however dangerous and unwise that would be to use, is certainly possible.
- As this experiment tells, while a Real Life Hot Blade may look impressive in some stunt, cutting power is not much increased, even with incandescent 1000°F knife.
- There once was a practice called "Blood Tempering," in which a red-hot blade is inserted by stab-wound and/or anally into a slave or prisoner of war, as it would cool the sword at body-temperature. This supposedly made the blades much stronger, and always killed the stab victim in practice.
- Almost never used, actually. And because the human body has such a wide variety of liquids and materials, it invariably created a blade with a poor, uneven temper that shattered easily. The practice was almost never maintained for any length of time in any culture, despite a moderately common myth.