Shield

All gems have defense mechanisms, even ones that weren't made for fighting like pearls and zircon. It's a way to ensure survival, as gems are not like humans that can multiply as they like. Gems had the need to conquer built into their blood, from the moment they emerged on foreign planets ready to take their orders and spread, never resting until the universe was Gem ruled.

Diamonds are different though. They're made to command, larger than even fused gems. A Diamond is her own defense, undefeatable by all but other diamonds. Or so they thought.

Until Rose Quartz and her rebel infantry took Yellow Diamond by storm, shattering her.

On Earth, they don't think about Rose Quartz much. Peridot and Jasper had still been gestating on a long since destroyed planet, and Lapis was imprisoned, longing not for her diamond or her duty, but for her home.

Yet, they speak of her enough that Steven has nightmares of her. Rose Quartz bearing down on him with her shield and sword, ready to finish what Pink Diamond started. It is the nightmares that teach him how to summon his weapon.

He wakes up terrified, encased in diamond. He must have screamed, because Peridot runs in holding a bag of cheesy poofs in her underwear, her hand already on her gem.

He can't control his powers then, he's still terrified, grabbing at his gem like his hand can block a sword. He doesn't see her as Peridot for a moment, only an enemy in his home. The Diamonds branch out and pierce her.

Thankfully, her gem remains intact, falling to the floor.

He's even more terrified now, he's never seen them retreat into their gems, he knows she's okay, they've at least explained that much, but he's still scared, shaking and crying. His fear feeds the diamonds, they grow out further and further until the room is covered in them.

"STEVEN!" Jasper manages to yell loud enough for him to hear, her crash helmet on and banging against the diamond shield.

He doesn't know what to do, and Jasper's banging and shouting is upsetting him more, he's trying to hold back powers he can't control because he doesn't want to poof Jasper, he doesn't want to hurt anyone.

"I don't know what to do!" He screams, over and over while Jasper tries to break through.

It's Lapis who manages to calm him down. She sends droplets of water underneath the diamonds until she is has enough to make a clone of herself, who picks Steven up and rocks him.

"Bye and bye, the moons is half a lemon pie, the mice who stole the other half, have scattered star crumbs across the sky," She sang, rocking him back and forth until finally he calms, the diamond encasing them slowly crept back until finally they faded, the only proof of their existence in the cracks on the walls and Peridot's gem on the floor.

"What was that?" Steven sobs.

"That," Jasper declares, with a grin that twists her face into something wicked, "Is the power of White Diamond."