This was done for a Stealthy Stories challenge by Connie Nervegas, who wanted someone to do a rather pretentious oneshot about the parallels between Castor and Pollux and Raph and Leo.
I don't know about pretentious (it probably is) but here it is.
"Like Castor and Pollux."
"Hmm?" Leo turned to look at his brother. He'd been spacing, which was nothing new, but it appeared that Don had been as well. Don shook himself out of his book and gave Leo a brittle smile.
"You and Raph, I mean."
Somehow that name still had power to wound, even so long after the fact. Leo couldn't even really remember his brother's face, but the mere mention of his name was painful even now.
"How so?"
"Castor and Pollux, one mortal, one immortal. One destined to die, the other destined not to."
"I'm hardly immortal, Don."
His brother leaned back in his chair, heaving a great sigh.
"But it was always Raph that was going to go first. We knew that."
Leo was slightly affronted.
"I didn't know that," he protested. "I always thought it would be me."
Don gave him his sad smile that was the closest thing to laughter he ever came.
"And we knew that, too. But Raph was too passionate to live long. He'd find some way to go down in a blaze of glory. I always knew…"
Leo looked back out the window. He'd known it too, which was why he'd vowed to go first anyway. It hadn't worked.
"What happened to them?" he asked, seeking punishment. They were Greek, right? They had to have a tragic end.
Don snapped himself out of another reverie and spoke as if on autopilot.
"When Castor died, Pollux asked the gods to share his immortality with his brother. They granted his request, and now they're floating above our heads," he gestured, "up there, as a bunch of stars."
"Hm?"
"They're Gemini."
"Oh."
Was that a happy ending? Leo couldn't decide. Would Raph want to be a bunch of stars? Would he?
He preferred Japanese mythology anyway.