Lucina is a Lord in Fire Emblem: Awakening. With her world destroyed by Grima, the fell dragon she and other characters enter through the Outrealm Gate to go back in time in hopes of changing the future. Wearing a mask she arrives at a time when Chrom and the Shepherds are being attacked by the undead human Risen and saves them. She introduces herself as Marth before leaving the group.
She later meets Chrom in a battle to decide which Khan will become the leader Khan of Ferox as she represents the West-Khan Bastillo. It is then Chrom notices she wields a sword that exactly looks like his, though it is known as the Parallel Falchion. Chrom defeats her thus letting East-Khan Flavia become the leader Khan which leads to an alliance between Ylisse and Ferox for the upcoming war against neighbouring Plegia.
In an attempt to change the future she informs Chrom about the pending assassination by Plegia on their Exhalt leader Emmeryn. She gains Chrom’s trust by preventing an assassination attempt on him by slaying the assassin hiding in the bushes. Another assassin appears and attacks Lucina causing her mask to be destroyed revealing that she is a girl. The group prevents the assassination attempt and save Emmeryn. Satisfied that the future has changes Lucina leaves the group.
However, Plegia later kidnaps Emmeryn with the demand for Chrom’s Fire Emblem or they plan to execute her. After a failed rescue attempt Emmeryn sacrifices herself to prevent Chrom from handing over the Fire Emblem. It is then Lucina, who has reappeared, realizes that the future has not changed, just the path in which it flows. Chrom would later kill the King of Plegia, winning the war.
Two years later and news that the Empire of Valm is crossing the ocean to take over the continent Chrom, the new Exhalt reignites the alliance between Ylisse and Ferox. Being outnumbered he seeks help from Plegia despite not trusting their new leader. Their leader, Validar agrees to send supplies. Chrom is attacked by Risen which Lucina appears and saves him. Lucina decides to join to team permanently.
With the knowledge that the future is approaching she attempts to change it by preventing Bastillo from challenging Walhart, the conqueror of Valm as he would die. He still decides to go and stall Walhart while Chrom’s troops attack the south. Bastillo still dies, again failing to change the future. Chrom decides to finish Walhart once and for all, killing him and winning the war.
After the war Chrom meets with Validar who claims to have a gemstone for his Fire Emblem. It is then Validar who controls Robin (the Avatar) to give him the Fire Emblem so he can use it to resurrect Grima. It is then Lucina confirms that Chrom will be killed by Robin and attempts to kill him herself to change the future. Chrom stops her saying that there must be another way.
While they are successful in preventing Chrom’s death and killing Validar the future again refused to change as Grima is resurrected. The group sets out and kills Grima, finally saving the future.
"Let us fight with honor. May the best soldier win!" - Lucina