"So this is a daemon, is it?" Kneeling, he stops just short of reaching out and running a finger across the soft fur on Lycus's back- and, quite frankly, Rose wouldn't have minded if he had. "
Acrobates pygmaeus, the Feathertail Glider or Flying Mouse- fascinating!"
"Where's Idris?" Lycus's tail curves up like a question mark. The Doctor's demon is a sleek Amur leopard, agile and light on her feet. To Rose, he adds: I haven't seen her since the Nestene consciousness tried to destroy the Tardis.
He grins. "Here."
"Where's here? You didn't even point or anything. "
"The Tardis." Reaching the console in two exuberant bounds, he runs a hand over its surface, as if petting a cat. "Time Lords' daemons are their Tardises- Idris only turns part of herself into a leopard so that I can have her with me when we're exploring. Her chameleon circuit is broken- otherwise she'd still be able to shift-"
"Wait. So are we, like, violating you?" In an attempt to touch as little of the floor as possible, she stands on one foot; Lycus scampers halfway up her leg.
The Doctor grins. "Nope," he says, popping the P. "Only thing I feel is if somebody touches the console- or Idris's fur when she's in cat form, but that's it."
One month later, he teaches her how to fly the Tardis.
When Rose's eyes glow Time-Vortex gold, light spills from her and into Lycus, particles of radioactive glitter forcing themselves through every strand of fur. Before Idris can reach him, he convulses, changes, grows, until the flying mouse part of him is only a tiny speck in the torso of an enormous, incandescent-furred wolf.
"I can see everything," Rose says. "All that ever was. All that could be."
Lycus's eyes lock onto Idris's. Help me.
The Tardis's new aspect matches the Doctor's new body perfectly. A ring-tailed cat, with a small frame, soft fur, and enormous, dark brown eyes. Idris- who is no longer Idris, but still, apparently, Idris- curls around her Time Lord's neck like a scarf.
Rose cradles Lycus close to her chest; the flying mouse still bristles with the fury that his human has managed to shove aside. "Can you change back?"
"Do you want me to?"
"Yes," Lycus blurts out.
"Oh."
She fills the ensuing silence before it can occur. "Can you?"
His gaze shifts upwards. "No. Do you want to leave?"
Lycus recoils. "Do you want us to?"
"No," a small voice says. And Idris leaps from the Doctor's shoulder to settle on Rose's own.