Run
They've spent their whole lives running; in fear or just for the joy of living, it varies. Neither of them consider anything else; no other way of life occurs to them. For them this is how the universe works; they've never known any different.
This first time, then, the first time they realise that their lives aren't like those of any other creature in the vast expanse of the multiverse that they call home, is a wake-up call.
They've been gods before, worshipped and feared in equal measures, held the power of creation in their hands long before they were strong enough to bear the responsibility, and long before they were cynical enough to use it for their own gain. They've been hated too; sworn at, hissed at, and loathed for no other reason than their existence, but for most of their lives they've been loved and loved in return, and for them running has always been a game.
This is the first time they realise it's not.
Blood has been spilt already, and lies in slick puddles as they throw themselves down corridor after corridor, not noticing the pain of bashed elbows and twisted ankles, only aware of the clamminess of their hands as they cling to each other - first one leading then the other - but always together. The screams and cries that follow them are drowned out by the sounds of their own terrified heartbeats.
There's no breath for conversation, even if there was the time, even if they knew what to say, and the link between their minds lies silent; hollow. Their palms slip together as they turn another corner, and slide apart as the boy spins round, pushing his sister behind him into a doorway that leads to who knows where. She calls for him, as best she can, and in return he begs her to run, run anywhere, run faster without him, and through his own fear knows that he has to keep her safe. Unarmed, he turns to face the darkness, and before she can reach for him, the doorway is closed.
The hollow space in her mind seems to ring out, the silence filling her ears with buzzing and her insides with an awful sickness. All her life he's been there. Now he's gone.
When they find her she's still screaming his name.