Red haired and slender, Eowyn was the eldest of the children of Haruka of Harad and Gendo of Amber. She was noted for being very emotional, very brave, and very energetic. Her life was quite short, as she died in 624 during her first major battle. The Cimbri Wars were in full swing and Eowyn pressured her superior officer, General Marduk, into undertaking a winter offensive, using her position as a princess as club, despite him being theoretically her commander.
The result was a disastrous battle on Lake Harad, which was frozen over. The lake broke open during the battle, possibly due to the use of magic or intervention by supernatural forces, and the Cimbri scored a major victory. General Marduk and Eowyn both died. Afterwards, the Cimbri swarmed over much of western Harad.
There is some reason to believe that Haruka's five children, if they had all lived to maturity, might have become the Children of the Elements of that era, with Eowyn as the Child of Air, but this did not come to pass.
During the Annadil Crisis, a woman appeared in Harad, claiming to be Eowyn, arming her troops with gunpowder weaponry. She vanished after Annadil's death; however, an "Eowyn" who claimed to be "an Amberite who saw the light of the Serpent" later turned up in the faction of Serpent's Horn rallied by Daffyl, and she was indeed the same woman who led the revolt in Harad, 40 years ago. Her attempt to use a pistol (it missed the mark, but it -did- go off, despite the shadow being barred to normal gunpowder) during the final altercation between the hostage rescuers and the leaders of Serpent's Horn only adds further evidence to what has been learned. She has since been captured and incarcerated up in Ember.
Further investigation and questioning by Queen Corrine and her staff has revealed that this "False Eowyn" is actually a blood-creature made from the original Eowyn's blood. Who did this is unknown; the only thing known for certain is that the samples would have needed to been taken around 624 AY, while Eowyn's corpse was still fresh. Despite her origins, she bears the Blood of Amber and a full Air Pattern imprint, having walked Tir'Na'Nog's pattern multiple times. She also bears an unreasoning hatred for Prince Drake, believing him to have engineered the death of the other Harad sisters and Haruka so that he could be relegitimized during the days of the Cimbri and Alan wars. It is the opinion of Queen Corrine and Kanna that this Eowyn was raised in a Flawed Amber by some outside party (likely Sakura) before being set loose upon the world, since she has no evidence of mental tampering to create a false history (which would have been wiped out with multiple pattern walks, anyway). She later joined the Serpent's Horn, and was a longtime member of that 'august' body; she was also provided Amber Gunpowder by Annadil during the latter days of the Annadil Crisis.
Despite Eowyn's tragic history, and longtime involvement in a terrorist organization, it is hoped by Queen Corrine that one day she will be able to see through the lies she has been fed throughout her life, and be able to rejoin her family. It is the Queen's opinion that the blood-Eowyn has lived for so long, independantly, that she should now be considered a full person, and given the same chances as the rest of the family to acheive redemption.
After a meeting with Princess Motoko, Eowyn has repented her past, and joined the defense of the Chaos mission on the Day of the Dead, where she fought nobly and well. She also had a tryst with Kuno of House Alars, which is unlikely to be repeated given her past with said house...
Eowyn Arisugawa, Commander of the Palace Guard of Castle Ember, bears a great physical resemblance to the original Eowyn and her duplicate, save with a much more pronounced tan.