With Yukio's demonic powers awakening, Rin knew of and noted immediately the changes in Yukio. He saw plainly the new slant of Yukio's eyes, the angling of the tips of his ears, and the sharpening of his incisors, but it wasn't until he and Yukio got back to their shared dorm that it sunk in. It wasn't until he saw Yukio shimmy out of his slacks and his tail, slender with a frizzy tip, come into view that it really sunk in.

Now, Rin is watching Yukio intently, surveying the movements of his tail. He looks at his own tail, realizing that he never spent much time thinking about it. To him, once it was there, it was as if it always had been. There wasn't much else to it.

Yukio can feel Rin's gaze burning into his lower back as he shrugs off his shirt. He turns to the side, tail twitching irritably as he fixes Rin with a long-suffering look.

"Please stop acting as though you've never seen a tail before, nii-san," Yukio says. He has that tone to his voice, the one that is like a steel baseball bat wrapped in satin. "It's weird of you to stare."

Embarrassed, Rin plays it off with a grin and a shrug. "Sorry. It's just different on you, Yukio."

That gets a small smile from his younger brother, who pulls a tee over his head to replace the uniform shirt he took off. "Tell me about it."

Weeks later, curiosity is eating away at Rin's ability to not openly stare every time Yukio's tail makes an appearance. He keeps visually comparing it to his own. Yukio's tail seems slightly shorter, only reaching to mid-calf when it's wrapped around his leg, as opposed to Rin's own tail, that reaches his ankles. It's sleeker at the end, looking less like the bushy wolf's tail that he calls his own.

It's the subtle differences that keep Rin entranced. He can read his brother's emotions better now that they translate into his tail. While Yukio is studying, the tip of his tail sweeps across the floor. When he's sleeping, his tail is loosely wound around his right thigh. Always the right thigh, Rin notices. When he's angry, it puffs up – one thing they both have in common – and when he's annoyed and six seconds from smacking Rin upside the head with the nearest object, his tail swishes violently from side to side.

Rin thinks he may know more about Yukio now than he ever did. Still, there's one or two things he'd like to know that he can't get just from eyeing Yukio every free chance he gets.

Yukio is already at his desk, face down in a book, when Rin enters their room. The first thing Rin does, after kicking off his shoes, is plop a bottle of mineral water down on Yukio's desk. Yukio looks at the bottle, looks at Rin, smiles, and then focuses back on his book.

"Thank you for remembering," he says.

"No problem," Rin responds. He fishes his own drink out of the plastic bag he brought with him and flops down in own chair.

The next few moments feel awkward to Rin. His plan, as haphazard as it is, was to present Yukio with the mineral water to show he's an awesome brother, and then ask in the least embarrassing way possible if he could touch Yukio's tail. He can't get the words out of his mouth, though. It isn't that he's afraid – Rin can't remember the last time he felt pure fear – he just doesn't want Yukio to think he's weird. Weirder. Whatever.

Despite all the back and forth going on in Rin's head, when Yukio brings the opening of his water bottle to his lips and his tail curls, just slightly, around the leg of the chair he's sitting in, the words come tumbling out of Rin's mouth like an avalanche.

"Can I touch it?"

Yukio swallows and turns to look at Rin. "Touch what?" he responds, then swallows again.

Outwithit, Rin tells himself before Yukio goes back to studying. His little brother is going to be the death of him. Literally.

"Your tail. Can I touch your tail," Rin says. Surprise is written all over Yukio's face. Seeing that, Rin amends sheepishly, "I'm not weird, okay?"

Yukio replaces the cap on his water bottle and can't help but laugh. Of course Rin is weird. Hell, everything about the both of them is weird. That just can't be helped.

"Alright," Yukio says, getting up from his chair to stand in front of Rin. "I'll let you, but only if you promise to stop staring at me all the time. You're really bad at hiding it."

"Okay, okay, I promise," Rin mumbles. Sometimes he feels like he should be the younger twin.

Yukio turns his back to Rin and Rin touches Yukio's tail gingerly. He cards his fingers through the fluffy hair, marveling at the softness. He glides his fingers further up, all the way to the base of Yukio's spine and back down again. He can feel each ridge of the cartilage that makes up Yukio's tail and he squeezes, gently, which elicits a soft sigh from his brother.

"Hurts?" Rin says, squeezing again.

Yukio shakes his head, even though Rin's not looking up. "No."

Yukio tries to hold his tail still while Rin examines it, but Rin is making him feel jittery and off-balance. Little jolts of pleasure make his fingertips tingle and his breathing speed up. He's lost track of how long he's been standing here, but he feels keyed up; as if he needs Rin's touches to either stop or be more.

He's mostly sure he doesn't want it to stop.

Rin looks up when he hears his name from Yukio, pausing in his exploration. Yukio is looking at him over his shoulder, a flush riding high on his cheeks and his eyes dark and wide. Rin knows the expression on Yukio's face, has seen it before in magazines that he wasn't supposed to be reading and television that he wasn't supposed to be watching.

For a moment, he's paralyzed. Yukio's statement snaps him right out of it.

"Keep going, nii-san. Finish what you've started."

Rin can't say no.