Felicia is the daughter of Kilma, the leader of the Ice Tribe. And like all children of the Ice Tribe, she learned to wield ice powers and acclimatize to the frigid environs of her home. Early in her life the Kingdom of Nohr sent its agents to kidnap her and her older twin sister Flora. This hostage-taking on Nohr's part was a means to dissuade the Ice Tribe from carrying out an insurrection against King Garon. But unlike Flora, Felicia never thought about the political context behind her abduction.
Perhaps the main reason for her inability to see herself as a prisoner was due to her enjoyment of her new home in the Northern Fortress. There she became a part of the castle staff as a domestic servant, although her clumsiness prevented her from being as proficient a maid as she wanted to. Ironically she demonstrated better potential as a combatant, due to a combination of natural talent and strict combat training on the part of the veteran knight Gunter. In that regard she became the antithesis of her sister, who was a far more capable domestic servant than a fighter; both siblings came to envy the other for their respective strengths. Felicia also loved working for her master Corrin, who treated her as a friend and equal despite their different stations. Their bond strengthened further when the maid-in-training used her ice powers to alleviate her boss' fever, at the risk of her own health and well-being.
Felicia plays a relatively minor role in the overall Fire Emblem: Fates story, since her primary role is to serve her master regardless of their decision to side with Hoshido or Nohr. However, her presence in the campaigns varies depending on the gender of the player character. If Corrin is male, Felicia becomes one of the earliest playable characters who fights alongside him from nearly the beginning of any campaign to its end (save for a brief absence in Chapters 4 and 5). If the player character is female, Felicia joins Corrin's squad roughly in the middle of the campaign.
But the clumsy maid has a particularly traumatising moment in the Birthright campaign. At one point Flora, who encounters Corrin and his Hoshidan allies in one of KIng Garon’s villas, suggests that they should retreat to the land of the Ice Tribe to rest and recuperate. But this invitation becomes a trap, as the player character and their forces find themselves fighting Flora and the other tribesmen upon arrival. After the skirmish, Corrin and Felicia learn that King Garon ordered the Ice Tribe to seek and destroy his Hoshidan foes - with the threat of the Tribe's total eradication by the Kingdom of Nohr as the punishment for failure. Upon learning this piece of context, Felicia earnestly forgives his older sister. But Flora became so overwhelmed with shame that she commits suicide, by self-immolation, for everyone to see. This moment causes Felicia to briefly suffer a mental breakdown. But she eventually comes to accept her sister's death as reality and uses it as motivation to help Corrin topple King Garon.