It is the personal weapon of Brave Lucina.
Wielded by Brave Lucina, this lance passively boosts her Defense by 3 and grants Atk/Spd +3 to all allies within two spaces of her that are wielding any weapon that is not a Tome, Staff, or Dragonstone.
As of the 3.9 update of the game, the first 4 Choose Your Legends units received a refine for their weapons, which includes Geirskögul. Any refinement to the lance adds effectiveness against dragons, and the special refine also grants Def/Res +3 to said physical weapon allies within her range, as well as a "Breath" effect, giving their special cooldown charge +1 per attack when a foe initiates.
Grants Def+3. Grants allies with sword, lance, axe, bow, dagger, or beast damage within 2 spaces Atk/Spd+3 during combat.