Lucina

"Lucina is a princess of the kingdom of Ylisse, the successor state to the now-ancient kingdom of Archanea, and is Chrom's daughter. She bears the holy bloodline of Ylisse's rulers, the exalts, who carry the power of the legendary dragon Naga and her holy gifts to humanity: the Fire Emblem and the blade Falchion; this power is signified by the presence of a distinctive Brand on their bodies, with Lucina's being located in the iris of her left eye.

The adult Lucina the game primarily features is a time-traveller from an alternate future, who travels back to the current timeline in Fire Emblem Awakening due to the fell dragon Grima and his legions of Risen zombies bringing her own world to ruin. to reverse this unfortunate event, she and other future children of Chrom's allies, the Shepherds, travel back in time to prevent the revival of Grima in Chrom's timeline and change the future. When she travels back in time, she initially hides her identity by tying her hair back and wearing a distinctive mask given to her by Gerome, one of her allies from the future, and adopting the name "Marth" from her famous ancestor. She runs into Chrom and the Shepherds, saving her aunt Lissa from the first of the Risen on one occasion and later dueling Chrom in Arena Ferox. Her disguise is ruined during an attempt on her aunt Emmeryn while defending Chrom, causing her to disappear, only to reappear two years later, again defending Chrom from an . She is accidentally revealed to be a woman after an unexpected assassin appears and cuts her mask off before being killed by Chrom. Later, she confirms that she is his daughter by allowing him to see the Brand of the Exalt in her eye, just like his newborn daughter. Lucina then joins the Shepherds to assist them in a new war."

via SmashWiki