Areadbhar was originally wielded by Blaiddyd, one of the Ten Elites who fought in the War of Heroes. The weapon releases its full power when wielded by a bearer of the Crest of Blaiddyd, granting the combat art Atrocity.
Prior to the events of the Tragedy of Duscur, the lance was carried by Lambert. In Fire Emblem: Three Houses, Rodrigue confiscates Areadbhar from one of Cornelia's generals in Fhirdiad. After reuniting with Dimitri after the ambush at Ailell, the Valley of Torment Rodrigue gives Areadbhar to Dimitri as a gesture of loyalty.
Areadbhar was a spear used by the Irish mythological figure Lugh, which he demanded as tribute from the Persian king Pisear. According to the Oidhe Chloinne Tuireann (Ode of the Children of Tuireann), the speartip had to be kept submerged in water to prevent it from igniting.
Areadbhar's name is translated as "Slaughterer."