Mercurius

The Mercurius (ミラクルソード Mirakuru Sōdo, translated as Mercury Sword in the Japanese versions, and Miracle Sword in fan patches) is a legendary sword that appears in Fire Emblem: Ankoku Ryū to Hikari no Tsurugi, Fire Emblem: Monshō no Nazo and Fire Emblem: Shadow Dragon. It was taken by the Grust forces, but was later retrieved for Marth's army by Est. In Monshō no Nazo, Astram wields Mercurius. The player receives it if he joins their army, or if they kill her.

Fire Emblem: Ankoku Ryū to Hikari no Tsurugi

 * Mercury Sword
 * Sword
 * 24
 * 18
 * 100%
 * 10%
 * 1
 * 1
 * Marth only, increases growth rates.
 * }
 * Marth only, increases growth rates.
 * }

Fire Emblem: Monshō no Nazo

 * [[File:Miracle_Sword_FE3.png]]Mercury Sword
 * Sword
 * 12
 * 24
 * 20
 * 100%
 * 0%
 * 1
 * 4
 * 24,000
 * Doubles experience gain.
 * }

Fire Emblem: Shadow Dragon

 * [[File:Mercurius.png]]Mercurius
 * Sword
 * A
 * 20
 * 18
 * 100%
 * 10%
 * 1
 * 8
 * 2
 * }
 * }
 * }

Fire Emblem: Shin Monshō no Nazo ~Hikari to Kage no Eiyū~

 * [[File:Mercurius.png]]Mercurius
 * Sword
 * A
 * 20
 * 18
 * 100%
 * 10%
 * 1
 * 2
 * 0
 * }
 * }

Fire Emblem: Awakening

 * Mercurius
 * Sword
 * A
 * 25
 * 17
 * 95%
 * 5%
 * 1
 * 0
 * }
 * }
 * }

Etymology
Saint Mercurius was a Christian martyr whose name meant "wielder of two swords". It was said that his second sword was a gift from the Archangel, Michael.