A hundred dementors were advancing, gliding toward them, sucking their way closer to Harry’s despair, which was like a promise of a feast. . . .

He saw Ron’s silver terrier burst into the air, flicker feebly, and expire; he saw Hermione’s otter twist in midair and fade; and his own wand trembled in his hand, and he almost welcomed the oncoming oblivion, the promise of nothing, of no feeling. . . .

And then a silver hare, a boar, and a fox soared past Harry, Ron, and Hermione’s heads: The dementors fell back before the creatures’ approach. Three more people had arrived out of the darkness to stand beside them, their wands outstretched, continuing to cast their Patronuses: Luna, Ernie, and Seamus.

“That’s right,” said Luna encouragingly, as if they were back in the Room of Requirement and this was simply a spell practice for the D.A. “That’s right, Harry . . . come on, think of something happy. . . .”

“Something happy?” he said, his voice cracked.

“We’re all still here,” she whispered, “we’re still fighting. Come on, now. . . .”

There was a silver spark, then a wavering light, and then, with the greatest effort it had ever cost him, the stag burst from the end of Harry’s wand. It cantered forward, and now the dementors scattered in earnest, and immediately the night was mild again, but the sounds of the surrounding battle were loud in his ears.

Harry Potter and the Deathly Hallows – J.K. Rowling