A/n: More information in the first proper chapter.
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Prologue
"I've missed you," she whispered after a long while, her head buried into the curve of his neck, so softly he barely heard.
There was something painfully solemn behind her words, and he understood precisely why; perhaps they were the only two that ever would.
She slid into the space between his arm and ribs, pressing herself up against him in the warmest of cuddles.
"I wish we could stay like this forever. You, me, here."
He pressed his lips to her forehead. "Me too."
But they both knew he couldn't. Not now, not forever.
Their worlds are held apart by invisible strings; of barriers and pillars vibrating at different resonances, preventing the worlds from impacting upon a course of direct collision. But upon each of Barry Allen's visits, the strings are stretched thin, and the barriers and pillars shake as a result of his forceful intrusion into her world.
His abilities went against the force of nature, and as a result of his defiance, there came the repercussions.
Left alone, the strings will hold. But to continue traveling between those worlds, would be to doom them all into a path of direct collision.
And Barry Allen knows, as he sees how peaceful, how beautiful she is, that there will come a day, where he'll have to choose between risking the fate of two worlds, and seeing Kara Danvers for just one more day.
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