The Fire Emblem is an eponymous concept at the core of the Fire Emblem series that takes a different form in each of the franchise's multiple universes. It is, in general, a physical item of great significance or power, and depending on the universe in question, may also play a role in the gameplay, as well.
In Fire Emblem: Ankoku Ryu to Hikari no Tsurugi and its remakes, the Fire Emblem is a shield owned by Princess Nyna and the rest of the Archanean royal family. Early in the game, she gives it to Marth, the only character able to equip it. It allows him to open chests, similar to the thief class.
In Monshou no Nazo and its remake, the Fire Emblem is split into twelve Zodiac Pieces and scattered across the continent. Marth collects these pieces and brings them to Gato, who reassembles them into the Fire Emblem. The Emblem also has slots for five orbs, which the player also gathers throughout the game. Hardin holds the last one, and after taking it from him, Marth is ready to face Medeus. During the battle against Medus, the Fire Emblem dispels all Earth Dragons that he summons each turn.
Because the continent of Jugdral exists in the same world as Archanea, the Jugdral titles Fire Emblem: Seisen no Keifu and Thracia 776 do not have a Fire Emblem of their own.
The Fire Emblem of Elibe is the national seal of the nation of Bern.
The Fire Emblem of Magvel is the sacred stone of the nation of Grado.
In Fire Emblem: Path of Radiance and Fire Emblem: Radiant Dawn, the Fire Emblem takes the form of Lehran's Medallion; a bronze medallion in which a legendary dark god has been sealed. It is said that the god will awaken should the continent of Tellius become engulfed in warfare. The medallion plays no gameplay significance in either game.
In Path of Radiance, the medallion is initially in the hands of Mist, Ike's sister, who received it under the belief that it was an heirloom. The medallion was originally kept by a member of the heron laguz clan who passed it to Elena, Ike and Mist's future mother, for safe keeping. After Elena died, Greil gave it to Mist and established a strict rule that no one other than Mist was allowed to touch it. Only those with a purely balanced spirit such as she are capable of holding the medallion without losing their minds.
In the present, however, King Ashnard of Daein plots to summon the dark god within by igniting a war and claiming the medallion for himself. He launches an invasion of the neighboring nation of Crimea and sends his men in search of the medallion. Eventually, the Fire Emblem falls into his hands, but he is unable to awaken the dark god and is slain by Crimea's liberating army.
In Radiant Dawn, the medallion once again becomes a focus of attention. Through a complex web of conspiracy and manipulation, Sephiran manages to ignite a war capable of unsealing the medallion; however, his goal is not to awaken Yune, the goddess of chaos falsely labeled a "dark god" from her resting place, but rather the goddess of order Ashera, Yune's sister. In doing so, he hoped that Ashera would bring the judgment upon the people of Tellius he felt that they deserved.