Marna emerges in the OAV series "Servant Princess" as a pivotal political figure. She arrives in the conquered kingdom of Fiel just as Prince Viceard Balbacil, leader of the invading Valdland army and her step-son, secures victory over Prince Kwan's forces and captures Princess Erufina. Marna shares an entangled past with Viceard, having once been his first love before marrying his father, King Balbacil.

She delivers critical intelligence to Viceard, revealing his father's scheme to frame and eliminate him. This disclosure compels Viceard to reevaluate his position and strategy within Fiel. Marna's presence exerts a moderating influence on Viceard, tempering his conduct towards the captured women of Fiel, including Princess Erufina. Erufina herself observes a distinct shift in Viceard's demeanor during Marna's company, catching glimpses of a less severe, more contemplative side to the conqueror.

Amid growing instability fueled by King Balbacil's impending arrival and the escape of the wounded Prince Kwan, Marna's intervention and the intelligence she provides generate fresh tensions and shifting alliances within the occupied kingdom. Her actions directly impact Viceard's decisions and the destiny of the Fiel royal prisoners, acting as a catalyst for evolving dynamics among the central characters during the occupation.