The sun was dipping low, casting long, orange shadows across the dusty playground. Six-year-old Lucifer sat cross-legged in the sandbox, his small hands carefully patting down the last tower of their magnificent castle. Beside him, Nancy was decorating the gate with shiny pebbles she had found near the swings.
"We'll live here forever," Nancy whispered, her eyes bright with the kind of certainty only a child possesses.
Lucifer didn't look up. His throat felt tight. He knew his father's car was already packed with heavy brown boxes. In an hour, he would be on a plane, moving to a city across the ocean.
"I have to go, Nancy," he said, his voice barely a murmur.
Nancy stopped moving. The pebble slipped from her fingers. "But the castle isn't finished."
"Take this." Lucifer reached into his pocket and pulled out a small, chipped blue marble—his most prized possession. He pressed it into her palm. "Keep it until I come back. It's a promise."
Nancy looked at the blue glass shining in her hand, then back at her best friend. She didn't cry; she just nodded solemnly, closing her fist tight around the marble.
As the sharp honk of a car horn echoed through the park, Lucifer stood up and ran toward the gate without looking back. He didn't see the wind pick up, or the way a stray ball accidentally rolled over their sandcastle, crushing the towers into a flat, unrecognizable pile of dust.
The promise was made, but the world they built was already gone.