Marcia (マーシャ, Māsha) is a pink haired Begnion knight, who is first met confronting a group of pirates in her search for her older brother, Makalov in Chapter 3 of Fire Emblem: Path of Radiance: the pirates refuse to cooperate and Marcia tries to fight them off. She cannot be recruited in this chapter, but if Ike talks to her, she will leave and return in Chapter 9, where Ike has to talk to her again and she will join.
Marcia seems to be cheerful, yet she does have an angry side (mainly shown at her brother or enemies); despite this, she does love him. It is revealed in supports with Tanith that she was very good at and very loyal to her job. Commander Tanith had very high expectations of Marcia-even to telling the Pegasus Knight she could lead the Holy Guard.
In Path of Radiance, she appears to have some romantic interest in Ike, constantly addressing him as 'handsome'. However, there are no supports that result them in building any sort of relationship and in Radiant Dawn, she no longer shows any interest in Ike whatsoever.
Since she is meant to be the youngest of the Path of Radiance Pegasus Trio, Marcia reveals to be childish.