That first night in the new Lair, Mike falls asleep with a take-out box still in his hand, and Raphael isn't far behind. Master Splinter folds himself into Leo's bedroll, and then only Leo and Don are awake, sitting quietly, listening to the steady drip-drip that will soon become the familiar background noise of their lives.
"It's good to have you back," Don says, just loud enough for Leo to hear.
Leo shifts, nestling his head into the crook of Don's neck. "I missed you."
Don is quiet for a moment. Then he says: "I wish you had been here two weeks ago."
"I'm sorry," Leo says. "I should have been here to fight with you."
"What?" Don turns to look down at his brother. "No, Leo, two weeks ago."
"Huh?" Leo lifts his head, meeting Don's gaze. "What – what day is it?"
"July seventh," Don says.
Leo furrows his brow. "July – oh. Oh, Donnie, I'm so sorry…"
"Eighteenth rebirthday," Don says. He lifts his hand, raising an imaginary mug. "Here's to us, bro."
"We were right," Leo says. "We always knew we wouldn't all be here to celebrate it."
"We didn't celebrate," Don says quietly.
Leo's face creases into a question.
Don lowers his hand. "We just couldn't," he says. "Not without you."
"You should have," Leo says. "It's not like we get another one."
Don shrugs. "What's the difference? We don't know exactly which day it is anyway."
Leo looks away. "How long were you going to wait?"
"Until you came home." Don puts his arm around Leo's shoulders. "We – we really missed you too, Leo."
"It won't be much of a party." Leo twitches his hand, making a vague gesture around their new home. "We have nothing."
"We had nothing eighteen years ago," Don points out. "But that accident was the best thing that ever happened to us."
Leo's eyes turn downwards, looking through the catwalk to the barren space below. "Eighteen years ago we had nothing to lose."
"We had everything to lose," Don says.
Leo ponders this. "I don't see how."
Don moves his hand slowly up and down Leo's arm, and soft words come from him in the same rhythm. "Nam quodcumque suis mutatum finibus exit, continuo hoc mors est illius quod fuit ante."
Leo breathes, the same tempo as Don's touch, Don's voice, and trusts that his brother will explain.
"For if anything is so transformed as to overstep its own limits… this means the immediate death of what it was before." Don turns, resting his snout against the top of Leo's head, murmuring in his ear. "You have to die, to be reborn."
Leo closes his eyes, and smiles. "Happy rebirthday, Donnie."
He feels Don's answering smile against his skin, and they fall asleep, the prospect of a new life echoing in the dripping pipes.
Quote is from Lucretius, "De Rerum Natura".