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The Falchion (ファルシオン Falchion) is a divine "sword of light" of Archanea, forged by the Divine Dragon ruler Naga for mankind in order to better protect themselves against the threat of rogue dragons. It was adopted by the kingdom of Altea as one of their national treasures following its use against the Earth Dragon Medeus by the kingdom's founder, Anri, and has in the centuries since been famously used by several of Anri's descendants: Marth the Hero-King, the founder of Ylisse, and Chrom and Lucina of Ylisse.
1100 years prior to the events of Fire Emblem: Ankoku Ryuu to Hikari no Tsurugi, and 500 years prior to the formation of the Kingdom of Archanea, it was forged by Naga from one of her own fangs along with the Shield of Seals, in case mankind ever needed to defend itself from dragons, and was placed in the Fane of Raman with the Shield and Tiki, his newly-born daughter. In the year 498, during the fifth year of Medeus's reign of terror on the world, the hero Anri travelled to the Ice Dragon Temple under the guidance of Gotoh to obtain the blade, and used it to kill Medeus and end the Dolhr empire.
After the fall of Dolhr, Anri founded the kingdom of Altea, and the Falchion became one of its ancestral relics, passed down through the successive kings until, one hundred years later, it belonged to Cornelius, the fourth king. In the year 602, at the onset of the War of Shadows and Medeus's revival, Cornelius departed with the blade with the intent of fulfilling his destiny as Anri's descendant, but was killed in Gra's betrayal. Gharnef took the blade and kept it safe for the majority of the war. Two years later, the blade was retrieved from Gharnef's corpse by Marth, Cornelius's son, who used it to slay Medeus for the second time.
In the year 607, in the initiating act of the War of Heroes, the forces of the Holy Empire of Archanea invaded and conquered Altea while Prince Marth was on an expedition in Grust, and the blade was again taken by the resurrected Gharnef. It was not recovered until the last moments of the war where Gharnef was slain again, and from there Marth used it to again slay Medeus, now resurrected as a Shadow Dragon.
As the following millennia passed, over time the divine blessing of the Falchion waned, and the blade began to decay and lose its durability; as a result, it was continually repaired over the ages, with the hilt coming to take an entirely different shape as a result of these repairs. Eventually, it came into the possession of the royal family of Ylisse, the descendants of Marth, and was used by the nation's founder to defeat the Fell Dragon Grima.
By the time of Fire Emblem: Awakening, this weakened Falchion (封剣ファルシオン Sealed Sword Falchion) was inherited by Chrom, Ylisse's prince, and used in his wars against Plegia, Valm and the Grimleal; its full power was unsealed by Naga herself to facilitate Grima's defeat, transforming it into the Exalted Falchion. A second time-displaced incarnation of the Falchion, dubbed the Parallel Falchion, was brought back by Chrom's daughter Lucina from her disastrous future.
An identical but different Falchion exists on Valentia, forged by the dark god Duma for King Rudolf to use to imprison the earth goddess Mila. This Falchion eventually became the property of Alm, who used it to slay Duma.
Ankoku Ryuu to Hikari no Tsurugi, Shadow Dragon 
|| Chapter 5, Chest in Duma's Temple, Basement 1
Mystery of the Emblem, New Mystery of the Emblem
Shadow Dragon 
In a flashback in the first episode, Prince of Aritia, Cornelius was the bearer of the Falchion (rendered in the English dub as Falcion) as in the games during the Gra betrayal. He attempted to use it to fight Gharnef, but failed and was slain. The anime's visual depiction of the Falchion differs greatly from the games' depictions: its hilt is a steel-blue with a gold blade, and the sword crackles with electricity as Cornelius unsheaths it. During his attack on Gharnef, Cornelius uses it to parry some of the Imhullu tendrils launched at him.
In Super Smash Bros. Melee, Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS and Wii U, Marth wields the Falchion. Additionally, the silhouette of the Falchion is used as an icon to represent the Fire Emblem franchise as a whole.
In "The Great Cave Offensive", the Falchion appears as one of several obtainable treasures referencing other Nintendo franchises, worth 325,000 gold. In the English version of Super Star, it was just called "Sword" as it predated the international presence of the Fire Emblem franchise; the name "Falchion" was restored to it in Super Star Ultra.
As part of the Chrom and Lucina armor set crossover promotion, the Wii U version of Monster Hunter: Frontier G will feature the Falchion as a usable weapon. Chrom's armor set is accompanied by his basic Falchion (under the name 封剣ファルシオンI Sealed Sword Falchion I), while Lucina's armor set instead gets her Parallel Falchion variant (裏剣ファルシオンI Hidden Sword Falchion I); both are paired with the Fire Emblem as a shield and single-handed sword set.
Etymology and other languages
|Names, etymology and in other regions
|| Definition, etymology and notes
|| • Falchion
| • A medieval single-edged sword reminiscent of the scimitar or dao. It should be noted that the Falchion does not resemble an actual falchion at all. This name is used in all appearances from Super Smash Bros. Melee onward.|
• A corruption of the above; this name was used only in the English dub of the Mystery of the Emblem anime.
|| • ファルシオン
| • Officially Romanized as Falchion, previously as Falcion.|
• Sealed Sword Falchion; this term is used in reference to the Falchion's weakened initial state in Awakening, and the blade in general is still referred to as "Falchion" in any of its three states in the game.
|| As above.
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|| As above.
|| As above.
- ↑ "Owain: Hark! Your partner fang resists the remorseless arrow of time! It is infused with the breath of gods and the passion of ages. Should a thousand thousand years pass, it shall never know the red sleep!
Lucina: That one is simple. Falchion's blade will never dull or rust no matter how much time passes.
Owain: But where fang meets sinew, Falchion remains a mortal work. Even genius cannot hope to stop the turning of the great wheel! And so it is reborn with each generation; transformed, butever the same in spirit.
Lucina: Hmm... But parts of the sword other than the blade DO wear out over time. The guard and pommel have been replaced over the years, changing its appearance. But it remains Falchion still." - Owain and Lucina, Fire Emblem: Awakening
- ↑ Wikipedia: Falchion