I'll begin, its a fantasy story. The rest of you just add what you want and let's see where it goes.

"They're coming." Jayden intoned as he and his brother, Gregor, looked out over the castle walls. The sun shone down hot and heavy and inside his armor Jayden felt as though he were cooking.
"Don't sound so ominous." Gregor said, giving his brother a playful nudge. "What's it been, 10 years, 20 since last they came?"
"15 then. And what happened last time?"