Spontaneous Weapon Creation

You're up against the Big Bad, and he enjoys Playing with Fire. However, just burning stuff is a bit dull. So what does he do? He uses his pyrokinesis and creates himself a sword out of fire. Great...

But fear not! The Hero has a similar trick up his sleeve. From out of nowhere he's able to conjure a sword of his own and take the Big Bad on blade to flaming blade.

The idea behind this trope is a character with the power to create a weapon. This can either be the power being to create or otherwise summon a weapon, or creating the weapon is but one application of a power they already possess. As in the example above, one character could conjure a weapon out of thin air, while the other created his weapon by clever application of his fire control. Sometimes the character can turn this power Up to Eleven to create a Storm of Blades.

One common use of this trope, especially among the second type, is frequently seen in Tournament Arcs where weapons would otherwise be banned. The person who crafts the weapon will be use Loophole Abuse to claim that, since what they're doing is simply an extension of the power they came in with, it's allowed. It usually is.

People who do this will generally possess Elemental Powers. Compare Natural Weapon, which can also fall into the Tournament Arc Loophole Abuse noted above. Contrast Flaming Sword, which is usually an otherwise metal sword that's on fire, rather than a sword made out of fire. Can often come about by characters who possess Imagination Based Superpowers. Shapeshifter Weapon is the one formed from the wielder's body.

Compare Instant Armor and its subtropes for when this sort of thing gets used for defense instead of offense. See also Elemental Punch, when weapons are not in use. A form of Shaping Your Attacks and may or may not involve a Person of Holding. See Summon to Hand for calling existing objects as opposed to creating them -- weapons are the most popular application.

Anime & Manga

 * A few times in One Piece, with Logia users Aokiji and Kizaru Shaping Their Attacks.
 * Aokiji is An Ice Person, and by taking a few blades of grass and breathing onto them, he freezes himself up an Ice Saber.
 * Kizaru manipulates light, essentially enabling him to wield a Laser Blade.
 * Hiei in Yu Yu Hakusho Plays with Fire, and at one point uses this ability to create a sword made out of Dark Fire. He's reluctant to use this more than he can help though, since it reminds him too much of Kuwabara's Spirit Sword, which is, or more accurately became, an example of this trope as well (it started as him drawing the true power out of a piece of a blessed wooden sword, which became his Spirit Sword's handle; as he got stronger he eventually could just pull the sword out of midair, without the chunk of wood).
 * When dueling Touma in A Certain Scientific Railgun, Mikoto Misaka uses electromagnetism on the sand and dirt around her to create a Whip Sword out of iron sand.
 * Harumi Kiyama briefly draws an energy blade while fighting Mikoto.
 * Alchemists from Fullmetal Alchemist can transmute weapons using the mass of floors or walls, although not many alchemists ever actually do so.
 * The "sword of one's heart" from Revolutionary Girl Utena might qualify. It's a regular old steel sword, but you draw it out of your own chest (or your Love Interest and/or creepy stalker figure does it for you). I might be misremembering some of the details.
 * Many characters in Beet the Vandel Buster can conjure weapons called Saiga. Beet is unique in that he can create five, which were given to him by the heroes he admired.
 * Bleach has a few examples:
 * Every zanpakutou is basically this.
 * In general, kidou magic has a lot of uses. Some spells allow you to make energy-shaped blades and such. Of special note is Black Coffin.
 * 6th Gotei Captain, Byakuya Kuchiki, who creates somewhere between thousands to millions of petal-shaped blades. They can also compress to form complete swords.
 * 13th Gotei Captain, Juushiro Ukitake, whose zanpukuto can split in two for Dual-Wielding.
 * 1st Espada Coyote Starrk, who can create an energy sword in his Resurreccion form. His other half, Lilynette Gingerback, can pull a sword out of the horn on her head.
 * 4th Espada Ulquiorra Cifer, who creates lance-shaped weapons in his Resurreccion and Segunda Etapa forms.
 * 5th Espada Nnoitra Jiruga, who can sprout crescent-shaped axes from his wrists in his Resurreccion.
 * 6th Espada Grimmjow Jaggerjack, who can create 5 "darts" which fire from his elbows and scratch-mark-shaped blades called Desgarron in his Resurreccion.
 * Primera Espada 103, Cirucci Thunderwitch, who can create sawblade-shaped reiatsu blades in her Resurreccion.
 * Ginjou Kuugo of X-Cution who summons a BFS
 * And finally, The Hero, Ichigo Kurosaki himself, after he gains whole new powers. His Fullbring ability originally takes the form of a swastika-shaped weapon, then an energy sword, and finally an actual sword with funky armor.
 * Dragonball Z
 * Krillin's signature attack (though many of the other Z-Warriors can do it too) is the Destructo Disk--a concentrated disk of Ki energy thinned to a razor sharp tip. Frieza and Cell also have a remote-controlled variation.
 * While she may appear to be an example of conjuration, Erza from Fairy Tail is, in fact, weapon summoning. She has everything stored in a separate location and brings it up to her in battle. The straighter example is Gray and his Ice Make magic.
 * The Pandora from Freezing does this with their Volt Weapon.
 * In Puella Magi Madoka Magica most Puella Magi possess the ability - each summons a specific kind of weapon, though they can apparently be created in any size or quantity.
 * Cures Rouge, Lemonade, Mint and Aqua of Yes! Pretty Cure 5 create weapons out of their elements - a ball of fire, energy whips, energy disks/barrier and water bow and arrows.
 * The opening to Smile Pretty Cure seems to hint that Cure Beauty can create an ice sword.
 * Galvatron does this, supposedly through pure Energon power, in Transformers Cybertron.

Comic Books
"Gunfire One Million: Pain -- so bad! If I can just reach -- Medipak -- *BLAM* Aaaaahh!! Aaaah, no, I turned the Medipak into a gun! Gwant: That really is kinda lame.... Hitman: Imagine his personal life. Gunfire One Million: Oh God, I turned my ass into a hand-grenade -- *FOOOMM*"
 * As noted in the description, the rings of the Green Lantern can create anything the wearer can imagine. Weapons are just but one of many things they can do.
 * Psylock's "focused totality of her psychic power" in X Men
 * This is one of the many possible uses of Invisible Woman's force fields. In one X Men/Fantastic Four miniseries, she had a Mama Bear moment and used a force sword to slay a Brood queen in close combat, leaving the males of both teams rather shocked.
 * This was the super-power of the minor DC hero Gunfire, who could turn any object into a blaster or bomb weapon with his touch by channeling energy into or through it.
 * A DC One Million crossover in the Hitman comic mercilessly spoofed Gunfire and, by extension, this power, with a particularly inept future counterpart of the original version.

Film

 * In Spaceballs, it's possible that this is how schwartz weapons like schwartz swords work. Yogurt claims that the rings from which the schwartz weapons appear to come are really a Magic Feather.
 * In Thor the Frost Giants can form weapons out of the ice covering their body.

Literature

 * In The Wheel of Time, Rand occasionally creates a sword made of fire, though this is a rather inefficient use of the One Power.
 * In High School DxD Kiba's Sacred Gear "Sword Birth" lets him create magic swords with different elemental attributes in order to counter his opponents' powers.

Tabletop Games

 * Dungeons and Dragons in general has had a number of spells that created weapons (usually swords). They include Mordenkainen's Sword, Dimensional Blade, Enchanted Blade...
 * Greyhawk has a few more, such as Nystul's Crystal Dagger and Jaran's Prismatic Blade.
 * Forgotten Realms adds Acid Lash, Bone Blade, Chromatic Blade, Decastave, Fellblade, Flamespin, Forcelash, Vampiric Lash, Ghost Blade, Whisper Blade, and Black Blade of Disaster. Thunderlance looks and is wielded like a spear, but doesn't act the part (it explosively discharges on touch).
 * Al-Qadim has Sand Jambiya, Sand Sword and Wind Blade.
 * Dark Sun Sourcebook The Will and the Way added Psychic Blade -- semi-tangible effect shaped and wielded like a sword and doubling as a mental attack.
 * In 3.5 version Psionics, the Soulknife can create a sword using psychic power. (Psychic warriors can also call weapons, but it's not clear if that's creating something or psychoporting it from some abandoned armory or what.)
 * Both Cyber Knights and Mind Melters from Rifts can create Psi Blades.
 * Shadowrun. In older editions, a number of fans developed spells that created a sword (or other weapon) made of energy. One type was called a "Power Sword". There have also been varieties that are made of a specific element (e.g. fire, cold, etc.) and have the appropriate elemental effect (e.g. fire setting flammable objects on fire).
 * Ars Magica. The spell "Tooth of the Staff" can create a spear with a polished flint head.

Video Games

 * In The Elder Scrolls series you can use the "Bind [weapon]" spells to summon the most powerful generic equipment in the game for a while.
 * Archer in Fate Stay Night is able to summon his weapons out of thin air through some unknown means, unlike the other Servants who are always wielding theirs. Shirou eventually becomes able to instantly create swords from mana through his own freakish magic specialization. The exact nature of this power is complicated and takes up a great amount of expo-speak over the three routes,
 * Kassadin's Laser Blade in League of Legends is this for his Void powers.
 * Mortal Kombat: The Kori Blade that Sub-Zero uses as his weapon style from Deadly Alliance onwards is created by Sub-Zero himself using his ice-based powers. Frost, being Sub-Zero's protege, uses the same technique to produce her own ice weapons, though her relative inexperience means that she can only create a pair of small daggers as opposed to Sub-Zero's entire sword.
 * In In Famous you can buy the ability to generate electric "swords" from your hands in order to do more melee damage at the cost of draining energy.
 * In Blaz Blue it's implied that the Kaka Clan's claws are of this nature (as in they have the ability to produce them, rather than them being retractable). Taokaka (the only playable example of the species so far) seems to be able to produce them in a number of shapes.

Web Comics

 * The Stus of Dubious Company. Gary creates katars out of fire, while Marty can summon any weapon out of thin air.
 * For a long time in El Goonish Shive, women who were offended by sexist men could conjure hammers from out of nowhere and use them to pummel the offender. This lasted until
 * Susan can instantly summon a replica of anything from a specially marked container, and keeps a few cold weapons there. And when she finally got her own spellbook, it started with the old good stun-hammer -- without any limitations. So she remains "The Hammer Queen".
 * Abraham possesses spells that summon or create swords, shields, and axes.

Western Animation

 * In Avatar: The Last Airbender, Aang briefly discusses the idea of making a 'Wind Sword' this way.