I've read the passage in which Aragorn meets Eomer many times. Here is the core of it:
"Come! Who are you? Whom do you serve? At whose command to you hunt Orcs in our land?"
"I serve no man," said Aragorn . . . "the Orcs whom we pursued took captive two of my friends. In such need a man that has no horse will go on foot, and he will not ask for leave to follow the trail. Nor will he count the heads of the enemy save with a sword. I am not weaponless."
Aragorn through back his cloak. The elven-sheath glittered as he grasped it,, and the bright blade of Anduril shone like a sudden flame as he swept it out. "Elendil!" he cried. "I am Aragorn son of Arathorn, and am called Elessar, the Elfstone, Dunadan, the heir of Isildur Elendil's son of Gondor. Here is the Sword that was Broken and is forged again! Will you aid me or thwart me? Choose swiftly!"
. . .
Eomer stepped back an a look of awe was in his face. He cast down his proud eyes. "These are indeed strange days," he muttered. "Dreams and legends spring to life out of the grass.
"Tell me, lord," he said, what brings you here?"
That's not magic. In D&D terms, Aragorn has not cast a spell. That's a dramatic example of one noble gaining an audience with another.