A/N: Reviews are deeply appreciated. Set at some point after "War Stories," but before "Objects in Space." Rating is just for safety's sake.

Stress Test

"River's not on the ship. They didn't want her here, but she couldn't make herself leave. So she melted. Melted away. They didn't know she could that, but she did. River's gone. You're talking to Serenity."

I am testing the strength of Serenity's heart in time to Tchaikovsky, spin spin spin UP spin and I twist and tumble onto the engine room floor, my heel bursting red where a wire dug in. Miscalculated the trajectory, swans can't fly in a vacuum. But the engine, it's not dented like my shin. The heart keeps on spinning. Granted bare feet produce less pressure than heel-points but still, this is a satisfactory result. Serenity is tough. If only I had some diamonds to scratch with (the hardness is important to know, too).

Kaylee is at the door, shining so bright it hurts my mind's eye to stare. "The engine room's awful important, River. You ain't supposed to be down here."

"Ship heart pumping." Spin again with the cello saw, arms out, face up. Not a stress test this time, just illustration. Beat beat goes the heart, like my feet. "I can hear it breathe." She is still too bright to look at head-on. I spin into her chest and spread my fingers over her sternum where the light sputters. Burns my eyes. "You breathe, too. Serenity can take Tchaikovsky."

Her light flickers and she is closed to me, ever since I made the soldier brains burst out. She does not put her hand on my shoulders and shove me back, even though she wants to. Kaylee is too scared of her brains bursting.

"Your heart is the ship and the ship's heart can take pounding feet but you can't, can you?" I speak the words at her neck and they bloom like smoke over her jugular. "You are so soft."

She does grip my shoulders then and she pushes back but I see another world where she hugs me closer and I can taste her, soft neck light but that is not this and I always, always try to stay on the proper reality with her. So I focus, easy as chasing apples. I am two feet away and she is almost-crying.

"Serenity's heart can take it and I thought Serenity was your heart but it's not, really, is it? Your heart squishes. Serenity is your lover, maybe, but not your heart, and if it is your heart then it is just life support. I miscalculated. I tried to test the stress—" I spread my arms to take in the tabernacle, her ship's sacred stones, "—that it could take and it can take me, but you can't, of course you can't. Serenity and you are not synonymous. That was an obvious fallacy. I have made so many errors."

She is silent so I grab her hand, but she tugs herself away.

"Good. Survival instincts. Vital in developing organisms."

"River—"

"Get away!" It is easiest to scream because the color burns and it is so, so hard to stare at something so breakable. She does.

When Simon comes he picks me up and wipes the wet off my cheeks. I bury my face in his shoulder and whisper, "Don't you dare let me spin out your heart, you boob."

"Impossible," he murmurs into my hair. He is lying, but he doesn't know. That makes me feel as safe as if his assessment was accurate, so then I fall asleep.