Kamui's Tamayorihime in Arcana Heart, a sword that can cut through ether (Elemental substance) without damaging the physical body.
Arx Fatalis has you make one yourself - a longsword (or much less cool saber), cast of mythril in dwarven automated forgery, surface fused with black undestructible meteor powder, and enchanted with a dragon egg for penetrating power. According to the enchanted weapon in-game manual, the thing is the strongest theoretically possible blade.
How cool are the Eternity swords in Aselia the Eternal - The Spirit of Eternity Sword? They're outright gods. In fact, the universe was apparently once one huge sword that shattered into them, and they're trying to reform.
Baldur's Gate II had the memorable Liliacor, an intelligent sword that was Ax-Crazy whose best advice on getting rich is to kill someone rich and loot the body. Repeatedly. It also protected you from confusion spells....
Then there's Carsomyr, the paladins-only Holy Avenger sword you recover from the lair of a notorious dragon and which comes with a list of bonuses and anti-magic abilities as long as your arm.
beatmania IIDX 21 SPADA's primary theme is swords. It should also be noted that "spada" is Italian for "sword".
its own version of the Moonlight Greatsword called the Holy Moonlight Sword. In one form it's a One-Handed Zweihänder, in the other it takes on its Moonlight form, deals Arcane Damage, and can shoot Sword Beams. Its power is so great that looking upon it restores the warped and twisted Ludwig to some degree of sanity.
Ludwig's Holy Blade, an attempted non-magical copy of the Moonlight Blade: a regular longsword with a massive stone sheath that can combine into a BFS.
the Chikage, a Katana/Saber hybrid that can be coated in its wielder's blood for a massive power boost.
Reiterpallasch, a Rapier with a built in Pistol.
the Rakuyo, a sword and dagger that combine at the hilt to form a dual-lightsaber like weapon,
the Threaded Cane, a Sword Cane that splits into a serrated whip.
the Blades Of Mercy, a sword that splits into two short swords.
In Castlevania: Aria of Sorrow, Soma can obtain the Sword in the Stone... while it's still in the stone!, but there is the Claimh Solais. It's huger, shinier, faster, holier... One of the rare examples where the Infinity +1 Sword sucks compared to some other weapon.
The Moonlight Greatsword is a recurring item in FromSoftware games. In both Dark Souls and Dark Souls II, the sword's blows deal magical damage instead of physical damage and a strong two-handed attack will launch a Sword Beam of pure moonlight. In the first Dark Souls it can only be obtained by cutting off the tail of Seath the Scaleless, an insane albino dragon who practically invented sorcery. In the second game, the sword is crafted from the Old Paledrake's Soul dropped by the Duke's Dear Freja in New Game Pluswhich is heavily implied to be Seath's soul.
Deus Ex: Human Revolution, however, does not, because it would be redundant and anachronistic by the game's timeline. Why is it redundant? Adam Jensen already has hyper-sharp killing blades mounted in his forearms.
Doom (2016) The Crucible is made of argent energy. It has a hilt made of bones (including a skull) and runes running along the blade. It's heavily implied to have been used by Doomguy himself. Did we also mention that it has the ability to manipulate Argent Energy as well?
Doom Eternal You are given the aforementioned blade as a melee weapon that you have to charge up before use. It can kill any non-boss demon in the game with one strike. The design of the weapon is markedly different from the Crucible in 2016, and is implied to be the Slayer's original Crucible from his demon killing spree in Hell.
From the Dragon Age series we have Starfang, made from starmetal, Vigilance, which is made with the bones of an elder High Dragon and is arguably the most powerful sword in the series, the Celebrant, which is a two-handed sword used as a badge of office for "Toughest Warrior in the Free Marches" and has absorbed the awesomeness of its past wielders... yeah, Dragon Age likes this Trope. A lot.
Asala is another great example, being the greatsword belonging to Sten, forged for his hand alone and as a Qunari, is considered to be an extension of his very soul. Finding it for him causes him to actually smile and afterwards earns you his Undying Loyalty.
There is also Yusaris, the Dragonslayer, the sword so cool it's on the game's title screen. (The sword in the background of the title screen is the aforementioned Asala.)
Dragon Quest, Dragon Quest II, Dragon Quest III and Dragon Quest XI have Erdrick's Sword◊, also known as the Sword of Light or Sword of Kings: an ancient one-handed broadsword with a curved hilt resembling a Phoenix bird. It is forged from Orichalcum, shoots lightning bolts and can only be wielded by the lineage of the legendary hero. It has cut down lords of chaos, dragons, demon lords and gods of destruction.
Subverted in DQVI. The party finds that the way is blocked by a horrible monster, with its lair blocked off by soldiers. They go to the king, who's promised to give an ancestral sword called the Sunderbolt Blade to the monster's slayer. However, the monster is beaten before you can do so (and the sword goes to its killer), and by the time you meet up again the sword is nothing special.
Boethiah, the Daedric Prince of Plots, is typically depicted as wielding a cool sword in her female statues. (Boethiah's male form statues instead wield a massive battle axe.) Boethiah is also associated with the artifact sword Goldbrand, a fire enchantedkatana that is usually one of the best one-handed swords in the games where it appears. In Morrowind, it can be further upgraded (if you know how) into Eltonbrand, very much an Infinity +1 Sword.
Umbra is another artifact sword which traps the souls of its victims, and is usually one of the most powerful bladed weapons in the games in which it appears. It is also an Empathic Weapon which slowly takes over its wielder, until they become a Blood Knight calling themselves "Umbra". Either the wielder keeps slaying worthy foes and taking more souls for the sword, or the wielder is slain and the sword finds a new, stronger wielder. (Thankfully, nothing bad happens to the Player Character if he/she wields Umbra.)
Dawnbreaker is an artifact sword associated with Meridia, a Fallen Angel Daedric Prince with an extreme hatred for anything undead. It has a glowing "core" and makes any undead it slays explode in a fiery Holy Hand Grenade fashion which damages any other nearby undead.
Basic, unenchanted ebony and Daedric qualify. Ebony is theorized to be the petrified blood of the "dead" creator god, Lorkhan, and is one of the best crafting materials available. Ebony weapons are often quite simple-but-elegant in design, and are black with yellow/gold trim. Daedric weapons are ebony infused with the souls of lesser Daedra, and are usually the highest tier crafting material available. Daedric weapons are are grey-black with red trim and add on a more-than-healthy amount of Spikes of Villainy.
Bound blades are glowing ethereal weapons made of pure magic that can be conjured at will and typically have stats comparable to Daedric swords.
The National Weapon of the Cyrodiilic Empires has long been the Imperial Sword, the primary weapon of the Imperial Legion. Though very simple, it has been used to forge no fewer than three Empires in Tamriellic history. It is based on the Roman Gladius, though in practice and appearance, comes closer to the Roman Spatha instead.
In Skyrim, a character highly skilled in Smithing and Enchanting can easily create their own with whatever effects he or she desires. A Dragonbone Sword honed to "Legendary" quality with multiple damaging enchantments will easily be the most damaging sword in the game.
In the spin-off Action-Adventure game Redguard, the hero Cyrus comes into possession of the Soul Sword, a sentient longsword housing the soul of the Crown Prince of Hammerfell, Prince A'tor. It is able to move on its own accord (which proves very useful in the game's climax) and A'tor is able to telepathically speak with the wielder of the blade.
Fable III's main selling point is the fact, as you level up, you can form a basic longsword into one of these, it evolves depending on various factors and decisions you make, such as alignment, how much you use magic, how much gold you make, etc.
Any Final Fantasy sword that isn't just bought in a shop (and some that are, depending on the game). Double points if it's named after one of the other swords on the list (Excalibur and Masamune are everpresent).
Final Fantasy VI has the Atma (or Ultima, depending on the translation) weapon, which resembles a pink lightsaber and grows longer the more HP the wielder has.
In Final Fantasy VII, the Buster Sword is huge, but otherwise not very remarkable: not magic, not super sharp, just a big hunk of metal on a short stick. The real reason it's so important is mostly symbolism: it was made by Angeal's father for when he went off to join SOLDIER. Angeal passed it on to his successor Zack, and he passed it on to Cloud. It's sort of a way of saying "You're the new resident badass, good luck!"
Garland's sword in Dissidia Final Fantasy is not only so large that he has to drag it around since he can't hold it high, but it can split into two swords as well as turn into an axe, a lance and a whip.
Any Greatsword in Final Fantasy XII; they tend to look like they were forged from one piece of some metal we've never even heard of, and, due to being too big for a sheath, you carry it on your back, and when you put it there, it makes a clanking sound, like it's held there with a magnet.
The various swords featured in the Final Fantasy XIII games. Lightning's gunblades, which transform between sword and gun modes; Serah's bowswords that can transform into a bow; and Noel's dual swords, which combine into a spear. Caius's sword in Final Fantasy XIII-2 looks utterly wicked, and Lightning Returns: Final Fantasy XIII has the Shard Blade, a crystalline BFS that puts the Buster Sword to shame.
The Level 50 swords in Final Fantasy XIV all tend to look insanely cool, and most have a tendency to glow in some manner.
Fire Emblem Fates features three such swords split between Corrin, the protagonist, and their two elder brothers Xander and Ryoma. A few chapters into the game, Corrin gains the divine blade Yato, which chooses its bearer and is said will bring peace; it has no less then three different powered-up forms depending on which route you're playing but the absolute best version has to be in the third route Revelation where it becomes the Omega Yato and a chainsaw sword, though its Conquest and Birthright counterparts, Shadow Yato and Blazing Yato are no slouches either. Xander meanwhile wields the dark sword Siegfried, while Ryoma wields the katana Raijinto, which can shoot shadow and lightning bolts respectively. In the Heirs of Fate DLC chapters, all of the blades have passed to the children of their original bearers, with Siegbert wielding Siegfried, Shiro with Raijinto, and both male and female Kana having the Shadow and Blazing Yatos respectively before both become Omega Yatos in the final chapter.
The Zarach from GMOTA, a Doom mod. This magic sword has shiny looks and many cool mechanics. It can be powered up with arcane power to greatly increase its attack power. It can change its shape and perform many different attacks with the power of subweapons. Lastly, it's able to unleash a devastating one-hit kill attack by consuming spirit gems!
God of War II brought us the Blade of Olympus, forged by Zeus himself to end the Great War between the Gods and Titans.
Golden Sun and its sequel Golden Sun: Dark Dawn have a bunch of these. What makes them really cool is their "Unleash" abilities. The Kikuichimonji summons a demon swordsman that slices your enemies in half. The Masamune summons dragons made out of water to smite your foes. The Verdant Sword turns into a lightsaber. Phaeton's Blade impales the enemy with spears of light. The coolest ones by far are the ones only The Hero (Isaac, Felix, and Matthew) can wield. The Gaia Blade can summon an even bigger cool sword while the Sol Blade can summon a miniature sun.
Not to forget the three of them have Psynergy involving summoning giant swords to impale their enemies.
Gruntz has them as combat-specific tools. They look like pirate sabers and are the strongest melee weapons in the game, requiring only two hits to kill a grunt.
Sol Badguy of Guilty Gear has quite possibly the coolest sword ever. It's a sword that resembles a giant Zippo lighter, and it has a mechanism which loads incendiary bullets, and a small motor built into the handgrip. It also enhances the power Sol's inherent fire magic and light magic. Oh, and it can do this. What's this beauty of a sword called? "Junkyard Dog".
Icewind Dale has Pale Justice, a sword given to the church of Tyr by a devout worshipper. Looks like a plain longsword, costs like a plain longsword... and has a lengthy cool description describing how come a +4/+7 vs Evil weapon happens to look like that.
Kingdom Hearts: Keyblades in general, which are part key, part sword. A mystical superpowered weapon granting superstrength and reflexes on absurd levels as well as being able to open and close routes between parallel universes.
League of Legends is chock full of them, mostly of a BFS variety. One character uses Mind over Matter to wield her sword, but is not described doing that with other objects, so it is assumedly just with her blade.
In Legaia: Duel Saga, there are some very cool swords. Some are on fire (sorta), none of them are sentient, but at least half of the main character's many blades are just kickass and very original in design. Wish I could find some pics of them online for proof...
Legacy of Kain: Soul Reaver, in both of its incarnations.
The Legend of Zelda's Master Sword, which powers vary from game-to-game but these days is usually treated as an all purpose weapon for destroying evil. Most commonly, it has the "Power to Repel Evil," which is how you end up Playing Tennis with the Boss when the boss is the King of Evil. In The Legend of Zelda: A Link to the Past you can actually make it even stronger by tempering it (turning the blade red instead of blue) and some Honest Axe action will get you an all mighty Golden Sword. There is also the Picori Sword from The Legend of Zelda: The Minish Cap which is later reforged as the Four Sword which are essentially the same as the Master Sword and the Phantom Sword from The Legend of Zelda: Phantom Hourglass, which appears to be that worlds version of the Master Sword (down to similar aesthetics).
It should be added that the Four Sword can make 4 copies of its wielder, turning you into a small army.
Also from the Zelda series is the Biggoron's Sword, which is so big it takes two hands to wield, but out-does the damage of every other weapon in the games it appears in.
In many games since The Legend of Zelda: Ocarina of Time, the sword has a dedicated button unlike the other items, and has the widest array of uses out of all of them. Optional upgrades often add even more utility to it, such as shooting energy while Link is at full health or chargeable whirl attacks.
On the evil side, there exists a dark version of the Master Sword that was wielded by the Demon King Demise. When he was sealed away, the sword assumed a humanoid form named Ghirahim who plotted to unseal Demise.
The Windcleaver, for being a big-ass katana that shoots Razor Wind
The Royal Guard's Sword, for being a black and red replica of the legendary Master Sword that is considerably more powerful than the unawakened Master Sword (unfortunately, it has some of the worst durability of any weapon in the game
Thunderblades, Flameblades, and Frostblades, all rather self-explanatory and available in one-handed and two-handed variants
Maxim's swords in Lufia: Curse of the Sinistrals look like an ordinary longsword...with a massive flame-shaped blade attached to the business end. The game's incarnation of the Dual Blade is pretty damn awesome as well.
Mana Series: The Sword of Evil's Bane before the Master Sword, Herald, Gigas, Exacalibur, Masamune, and a thousand other names: the Sword of Mana. The latter games desribe it being instrument to slaying primortal evil and choas to create the world. It is wieled by the hero for the world's peril. More often than not the hero ends up with a rusted or broken sword in the final battle instead; it'll do.
MapleStory: Several of the higher level swords qualify. Special mention goes to Blue Screamer, Doombringer, and Heaven's Gate.
The whole world of Enroth from Might and Magic was destroyed when the Ultimate Fire Sword (Armageddon's Blade) came into contact with the Ultimate Ice Sword (the Sword of Frost).
In the campaign for Hordes of the Underdark, an expansion pack for the original Neverwinter Nights, you might stumble upon a talking longsword named Enseric. Be ready for a fight though if you plan on freeing him...
The Silver Sword of Gith, from Neverwinter Nights 2. The average Silver Sword is capable of lopping heads and arms off with ease, shearing right through most materials, in addition to astral projections and is litterally made out of a constantly shifting blade of liquid silver. And that is the average silver sword carried by a Githyanki Knight. The Silver Sword of Gith is the blade of the FOUNDER of the Githyanki, known for being so bloodthirsty that she actually had to be stopped by her most loyal retainer when she started picking fights with everyone. This is also bypassing the fact that it's a shattered weapon, held together by the very power of your character's mind, with a list of beneficial properties that outpreforms everything other individual magic item in the game.
Nobody else thinks the Dragon Sword and the Dark Dragon Blade from Ninja Gaiden are cool?
Nioh 2 boasts the Sohayamaru, a Sword of Plot Advancement based on the real life Seven-Branched Sword. The Sohayamaru is a blade made out of pure amrita and is the only weapon that can slay the Big Bad.
Almost all of the swords in Otogi: Myth of Demons are special in some way, wether it was used to seal a powerful demon, is a demonic blade that can kill anything it touches, or has a blade made of solid moonlight. All of the swords have some unique story behind them, in fact, the most normal sword in this game is a large katana designed for splitting helmets.
Dak'kon's Karach blade from Planescape: Torment: made of pure elemental chaos and shaped by the wielder's will, a character who's studied it claims that, with the right mindset behind it, it could cut holes in reality...or kill an immortal.
Honedge from Pokémon X and Y is a Steel/Ghost sword pokemon with an ancient spirit residing inside. Those who try to wield it get their life force drained, however. When it evolves into Doublade, it becomes... two swords. Doublade then evolves into Aegislash, a BFS which a shield that can change from a Glass Cannon into a Stone Wall and vice- versa.
The Godsword. An Infinity +1 Sword composed of four separate swords.
Silverlight, while not particularly useful at first unless you need to get up close and personal with demons, gets upgraded to a very good melee weapon at the end of a quest about... getting up close and personal with a demon.
The blurite sword is another sword associated with a quest, specifically bringing material to an NPC so they can forge a replacement sword for somebody else. Statisically it's nothing special, but its unique appearance and being exclusive to a single quest led many players into wanting one for themselves. Originally, it wasn't possible to do so without tricking the game into making an extra, since you were expected to hand the finished sword over to the quest giver. Later on the quest was changed so that completing it unlocked the ability to forge your own blurite sword, making this exploit obsolete and keeping it from being too irreplacable to actually use.
The Chaos Breaker returns in Shining Force II, but it's a bit less cool this time around, being unable to use the spell ability from the original game. It's even been renamed to "Force Sword" which is a hell of a lot less cool than Chaos Breaker.
In addition to several swords from mythology, Shin Megami Tensei has two noteworthy examples:
Shin Megami Tensei II and Shin Megami Tensei: Nocturne has the sword of Taira no Masakado. It carries especially heavy significance, being a powerful Neutral-path-exclusive weapon for Aleph to use in the former and the key to the mystical Bando Shrine and thereby Masakado's power in the latter.
There's also the best weapon in the first two Shin Megami Tensei games: Hi-no-Kagutsuchi, containing the spirit of the Japanese god of fire who was powerful enough to accidentally burn his mother Izanami to death.
Slain has the sword Bathoryn carries throughout the game, a powerful, magical blade that can encase itself in flames or ice as needed. In fact, the sword is the actual main character - the old warrior that carries it isn't Bathoryn, Bathoryn is the sword, a Living Weapon forged by Lord Vroll. The sword turns up again in Valfaris, which is to be expected, since Therion is another son of Lord Vroll and thus Bathoryn's brother.
Sonic and the Black Knight gives Sonic a sword called Caliburn. There's also Sir Gawain's Dual Wielding Swords, Sir Lancelot's sword, and Sir Percival's sword in the same game. To say nothing of Excalibur Sonic's sword as well...
The Star Dragon Sword/Zodiac Sword from the Suikoden series is pretty badass, and something of a Deadpan Snarker to boot.
In a slightly more comical example, Gon from the first Suikoden can upgrade his regular Sword into a literal Cool Sword and from there into the Very Neat Sword.
Summon Night: Swordcraft Story and its sequel both contain large swords of power. In the first game, you craft said sword from the other four swords that your father, Shintetsu, actually put his soul into and died making. You can choose to sacrifice your Guardian Beast for a more powerful sword and an easier fight, or let your companion live and have a slightly more difficult time. Either way, your new sword is big, blue, and kicks ass. You don't get to keep it after the end however. Then the second game gives you another, which is activated with your Mono Shift. It can shoot large energy bolts, but it's damaged while doing so. Slightly subverted in the fact that said sword is essentially the weapon you have crafted currently, with the same strengths and weaknesses. It's still badass, and it still can lay down the hurt quickly.
Super Robot Wars: There is nothing that Zankantou/Colossal Blade cannot cut.
Tales of Symphonia: Lloyd eventually gets a pair of extremely cool swords, so he can Dual Wield them. One, the Flamberge, is a Flaming butcher knife, that used to belong to his birth father. The other, the Vorpal Sword, that was made by his adoptive father, is made of ice and can slice through rock. Lloyd can also combine the two into the Eternal Sword, a purple BFS, that serves as his Limit Break.
Ludger from Tales of Xillia 2 has a modern-looking version of the falcata as his main weapon. And just in case that wasn't cool enough already, he uses two of them in Reverse Grip.
Team Fortress 2 gives the Scottish cyclops Demoman an unlockable sword, the Eyelander. It decapitates foes, and changes your health and speed based on how many people you kill, because it's haunted.
Some other swords have since been added to the game, mostly for the demoman, though the Eyelander remains the most iconic.
Terraria has plenty of cool swords to choose from, but the best example would probably be the Infinity +1 Sword, the Zenith. After all, what other sword allows you to obliterate your foes with a Storm of Blades from a distance via the mouse cursor?
Temjin, the titular hero in Virtual-ON series, although his sword also works as a gun.
Just check out any epic weapon in World of Warcraft. Rule of Cool seems to be how everyone wants to fight. There are even things like axes with spikes and skulls randomly strewn on it. Or for a sword example, Thunderfury, a sword longer than yourself that has random lightning jolts on it plus some... unique... cutting edges.
If we're going to mention axes and cool weapons... Arcanite Reaper HOOOO!
Frostmourne hungers...
The Ashbringer...
The Great Royal Sword of Stormwind.
The twin blades of Azzinoth, the very cool swords wielded by Illidan, or Thunderfury, a sword wielded by Thunderaan, lord of wind elementals, Ashkandi, greatsword of the Brotherhood, Zin'rokh and Jin'rohk... The list goes on.
Basically every single green quality (meaning it gives stats at all) sword in World of Warcraft from The Burning Crusade (first expansion) and up, and quite a few from Classic.
, katana
