Disclaimer: All credit for the world and basic plot, etc, goes to Tolkien. And the whole point of this being a "What if" fic is that the ending is NOT the same as in canon. So onward!

Oh, and yes- I view fanfic as a "guilty pleasure."

Firefoot fidgeted nervously. Éomer, too, was restless. He kept slipping his helm off to shake his mane of sweaty hair. Acutely aware that his uncle Théoden was restrained and unmoving, he scanned the faces of the other riders.
There. He wasn't the only one fiddling around with anxiety. That young man kept ducking his head, almost like a horse....... wait..... hiding her face!
Éomer started as he recognized his sister, and Firefoot nearly sprang forward. But the King suddenly called for the charge; pounding filled his ears and wind his face.
Éowyn. As his voice rose in the traditional battle cries, he couldn't help but strain to hear..... to hear her light voice. It must be there. It needed to still be strong. The armies of the enemy rushed closer, and Éomer could only think that this should not be Éowyn's death approaching.
He fought fiercely, twisting round in the saddle to parry and stab, guiding Firefoot to trample the enemy. But his breath was suddenly cut short, and he could no more sing the war songs.. then a moment of sharp pain struck, before his over stimulated mind could realize why.

..Théoden saw his nephew, restless and unable to stay still. The boy would make a fine, fierce fight. Out of years of habit- the children of Eomund were seldom parted- he glanced for the slender form of Éowyn. And he saw her.
Her pale hair was less like the gossamer it once was; she looked weary under the heavy armor. This was what war brought, this..
He closed his eyes in emotional pain. If she wanted this to be her end, then this end would be a grand end. The glory of the charge of the Rohirrim should be for her, stern shieldmaiden in deadly battle..
All of the king's energy, wrought over years of love for his family, refined by the delicate dynamics that had been all too disrupted of late, came to a head as he let out a shout and began the thunder down the plain.

"Éowyn!" Théoden struggled to stand next to his niece. Great drafts of powerful wind shoved at him, and the dark, deadly shape of a Nazgul spun in to land. "Éowyn.." The king gripped her hand, smiling, yet looking forwards still. "I trust in you. We can face this carrion together."

"No... no!" Éowyn screamed, not heeding anything else. She was acting like an upset child. She was a little girl again. Éomer was dead. She fell beside him on the bloody field of victory, far too deep in despair to shed tears. He should still protect her, he should still comfort her...
Aragorn came softly up behind Théoden, who stood with his head bowed. "The two of you faced many conflicts, together and apart. Éomer was a loyal and headstrong man. I know not if you are feeling guilt or sorrow, but the valiant son of Eomund would not wish it."
Théoden nodded mutely, stiffening until Aragorn backed away. He watched Éowyn, curled on top of her brother. Éomer looked so human, armor awry, hair tangled... You were young, you were the future. You should have done your part and lived to be the hope. Find joy and song and family, Éomer, my son.