Summary: John + Shayera = Rex. It's all very scientific. Based on "Ancient History."
John and Mari were married not long after what everyone called "The Shadow Thief Incident." Mari had commented to Shayera that John seemed oddly eager to get on with their life together, after having stalled for so long. Shayera had nodded, but didn't comment, understanding that John hadn't told Mari about his trip to the future. Shayera had protested, but Mari insisted that she come to the wedding. Shayera had sat at the back of the chapel, her heart bleeding but her eyes dry.
They'd had no children. They'd tried, but none of the scientific advances of the age worked for them. Shayera had once found Mari crying over the monitor station controls; a miscarriage she'd explained. Shayera had offered sincere sympathy, but it hadn't stopped John from scowling at her when she'd pass.
She knew, deep down in his heart, he blamed fate, destiny...her...for punishing him for not following the pre-appointed script.
Years passed, more than thirty in total. First John was killed, then Wally, then Mari. Diana returned to her island home. Bruce grew old and crotchety. J'onn didn't change. Clark and Shayera aged, but much more slowly than humans.
One average afternoon, Shayera made the choice.
She became a thief. A scientifically gifted thief, but a thief nonetheless.
Her DNA was easy to harvest. John's DNA was more difficult to collect, considering he'd been dead for over ten years. Fortunately, the transporter computers kept a cellular file of everyone ever transported. She stole a copy of John's very essence.
It was simple enough these days to graft an old DNA pattern onto a blank cell. That's how lost limbs and organs were re-grown so easily now.
Some nips here, some re-sequencing there...and two cells merged into one. Then they split. And split again. Shayera watched through the microscope as the scene repeated itself over and over until her entire field of vision was filled with replicating cells.
She transferred the tiny mass to an opaque incubation chamber and set the controls to automatically adjust nutrients and temperature as the new life started to grow.
The computer alerted her late one night that movement from within the pod had triggered the emergence sequence. She raced to the laboratory in time to hear the sealed incubator hiss open. The constant blip of the heart monitor, the only sound she'd heard emitted from the chamber for eleven months solid, went silent.
Her heartbeat stopped in that moment as well, waiting, listening.
A gurgle. A sputter. A cry.
Shayera shoved the incubator lid off and looked inside. Her son -- *their* son -- lay in a shallow puddle of blue goo, declaring to the world his lungs were fully operational. She lifted him from the encasement and cradled him in her arms, not caring that the nutrient gel would stain her clothes.
She offered her son her finger, and he accepted it into his mouth, quieting his cries. She'd have to prepare formula later. Right now, she just wanted to hold him, to hold the last -- the only -- piece of John she'd ever have.
"Rex," she whispered, her lips pressed to his sticky forehead.