Lucina was born to Chrom and Robin making her a member of the Ylissean Royal Family. Years after her birth Chrom and Robin give life to their son, Morgan. As a member of the Ylissean Royal Family, Lucina inherited the Brand of the Exalt, which surfaced on her left eye. As Robin’s daughter, who is a Vessel of Grima, she also inherited Grima’s Cursed Mark which surfaced on her back. Her childhood was full of love and warmth. She often spent her days with her family and friends. She was a beloved princess in all of Ylisse. From a young age, she showed a great interest in swordplay and was personally taught by her father, whom she developed an especially close bond with. She has bonded with Falchion, being one of the few members deemed worthy to wield it. With her mother Lucina learned how imbued her minimal magical capabilities with her swordsmanship. She often went on many childhood excursions with her brother and the other children of the Shepherds. 

At the age of fourteen tragedy befell her family and the world as she knew it. Tragically, Chrom was killed by his wife, Robin (possessed by Grima). This event heralded the return of the Fell Dragon Grima. Using Robin’s soul Grima was resurrected and reigned an apocalyptic hell on the world. His return resulted in death and devastation of half of Ylisse’s population. Lucina and Morgan were taken to safety and Lissa unfortunately delivered the news of their parents’ death. She passed on Chrom’s Falchion to Lucina as the only thing left of her beloved father. To everyone’s despair Grima subsequently continued to use Robin’s corpse as a puppet to further his corruption. The world was plunged into perpetual darkness. Risen ravaged the land destroying nature and civilization. Over time the land of Ylisse becomes scorched and barren. Within the first year the Shepherds took it upon themselves to defend the surviving population of Ylisse while trying to protect their families. Regrettably they died one by one leaving their children behind. The Children of the Shepherds were forced to take their parent’s place as defenders. They stuck together and looked to Lucina as their leader. With no other choice Lucina accepted the title and began her campaign of finding a way to eliminate Grima.

In all that time Lucina was forced to bottle her emotions. She never showed her true anguish for all the loved ones she lost.

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In the future, where she was originally from, Lucina and some of the other children arrive at Mount Prism. Despite the fact that she only possesses four of the Fire Emblem's Gemstones, the fifth having been lost, Lucina still hopes that Naga will grant her the ability to defeat Grima. She goes into the temple by herself and attempts to request Naga's aid, managing to summon Naga in the process. After conversing with Naga, Lucina reports to the others that while the Awakening Ceremony cannot be performed with only four Gemstones, Naga informs her of another way to save the world: go back in time to prevent Grima's resurrection. She is unsure if the rest of the children will go along with the plan, but Inigo is confident that they will place their trust in her decision, while Brady is less certain.
 

Some time later, Lucina explains the option to return to the past to the rest of the children at Ylisstol. Inigo, Owain, Severa, and Cynthia agree with the plan, while Brady, Gerome, and Kjelle wish to stay in the future, and Laurent, Nah, Noire, and Yarne are undecided. Lucina says that she will respect if anyone decides to stay, but she will go even if she has to do so alone. She also mentions that since the Outrealm Gate will open in three days, everyone will have time to decide what to do.
 

On the final day before the Outrealm Gate opens, Ylisstol is abruptly attacked by Grima and his force of Risen. Lucina manages to fight back against the Risen, but the soldiers fighting alongside her are killed when Grima arrives. Lucina attempts to stand her ground against Grima, who boasts of his victory and mocks the death of Lucina's parents. Grima moves in to finish her, but she is saved when Gerome pulls her to safety, aided by Cynthia and Noire. Lucina speculates that Grima must have learned of their plan to return to the past, and requests that Gerome drop her onto Grima's head to attack him. He does so, and Lucina manages to wound Grima by impaling him with Falchion before once again being pulled to safety by Gerome, forcing Grima to retreat. However, Lucina realizes that the rest of Ylisstol has been completely destroyed by the Risen, killing everyone but the twelve remaining children.
 

Lucina arrives in the burning village just in time to prevent Owain and Inigo from sacrificing themselves to aid the others. She tells them and the rest of the children that Ylisstol is beyond saving, and the only thing that they can do is flee. She silently apologizes to Chrom for failing to protect Ylisse before retreating to a nearby forest.
 

Lucina says to the children that while it is too late to defeat Grima in their future, they can still return to the past to save the world. Inigo and Owain anticipate saving the world and returning to the future, but Lucina admits that there is something she didn't tell them previously: she doesn't know if they can return to their world after leaving it. Lucina reaffirms that it is impossible to defeat Grima, and she will return to the past to stop him even if she has to do it by herself. She understands that the rest are still undecided, and asks that they meet her at Mount Prism by daybreak if they decide to go with her. Before she goes there herself, Lucina heads to the ruins of Ylisstol to say goodbye to her parents.
 

Lucina reaches Mount Prism and finds that no one else is there. She is saddened, but prepares to leave before she is attacked by invading Risen. Fighting by herself, Lucina realizes that she could only fight on previously due to her friends supporting her, and she thanks them for their help before tearfully strengthening her resolve to save the world, though she would rather not do it by herself. Just then, the rest of the children arrive to help, reassuring Lucina that they are all going together.
 

After the Risen are slain, Gerome offers to give Lucina a mask to conceal her identity when they go to the past. She initially chooses a pair of massive glasses before a disgusted Severa picks out a butterfly mask for her instead. Noire and Nah reflect upon Lucina's unconventional fashion sense before she begins to weep with joy, glad that they can all laugh together again. She also admits that she was wrong in claiming that she could do everything by herself, but Nah and Severa reaffirm that they'll always be together. The group realizes that Grima and the Risen are attacking the temple, and Lucina urges the others to go on ahead of her while she covers them. Putting on the mask, Lucina bids farewell to her world as she declares that she will change her fate.