It sits in a polished box of maple on a shelf next to Cas's bed.

The boys don't know that Cas has it. They probably don't even know that it is missing from the pile of crates they have been cataloging. But while Dean is teaching him the finer points of shooting a gun, Cas thinks about it. When Sam tosses him to the mat to teach him safe falling techniques, he is thinking about it.

And in the rare moments when the boys are both asleep or out getting groceries or otherwise occupied, he practices the ancient forms, training his muscles to follow the motions he has locked in his memory from ages long past.

And so, when Dean hands him a gun and matter-of-factly says that Cas gets to ride shotgun on this case, Cas hands the gun back.

"I won't be using that."

Dean's eyebrows fly up in surprise. "You're not a bad shot. I was just heckling you the other day."

"No. I mean I have something of my own."

And then he has no choice but to fetch the maple box and bring it to the library, where Sam and Dean wait with baffled expressions as he undoes the brass clasps and pulls out the black wooden saya.

Sam is the first to speak. "A sword?"

Cas nods. "A special one." He holds the sword so Sam and Dean could see the single sigil engraved upon the rounded crosspiece.

Dean leans forward, squinting. "Is that - Enochian?"

"Yes." Cas hesitates. "It…says 'cas.'"

There is a weighty pause. "And…why do you have a thousand-year-old Japanese sword with your name on it?" Dean asks finally.

"It isn't," Cas says quickly. "My name," he clarifies when both Dean and Sam look bewildered. "'Cas' means…aegis. Protector. Shield." He shifts his feet uncomfortably. "My name used to mean 'Shield of God.'" Shaking his head to dispel that thought, he draws the sword carefully. "This sword…it was granted by an angel to a man who dearly wanted to protect something. His family, or his village, maybe."

"Wait. Angels were sticking their fingers in Japanese pies?" Dean asks.

Cas shoots him a patient look. "If an angel hears a particularly moving prayer, he is not going to limit himself by religious symbolism," he says quietly. "Religion was created by man. Prayers are universal." He turns the sword so the ripples in the blade caught the light. "Only true samurai could wear katanas, but a wakizashi such as this would be short enough to be worn by the lower classes." He slides it carefully back into the saya and begins to tie it to his belt.

Sam clears his throat. "Um. No offense, Cas, but bringing a knife to a gunfight is…actually a well-known idiom."

"Yes," Cas agrees dimly. "It means being comically unaware of the disparity between modes of weaponry. It doesn't stop you and Dean from carrying two dozen knives between you."

"Yeah, but not a sword," Dean points out. "Do you even know how to use that thing?"

Cas completes the final knot that secures the saya and takes a step back, well out of the way of the boys. "Toss me that apple core."

Bemused, Dean plucks the apple core from the table, considers it for a moment, and then lobs it slowly in Cas's general direction.

In one single, swift motion, Cas draws the sword in an upward arc from its saya, and the two halves of the apple core fly off in opposite directions. It is difficult to hide the gratification Cas feels at watching the dumbfounded expressions on Sam and Dean's faces as he calmly wipes the flat of the blade on his jeans before resheathing the sword. "The way I see it, beheading something is just as effective as shooting it. And, considering the types of things we fight, probably more so."

Sam apparently regains the power of speech before his brother. "And…when did you learn to do that?"

With a small smile, Cas taps his temple with his finger. "Everything you've been teaching me is already up here. I just…have to get used to telling a body how to do it. Without cheating, like I could with a vessel." He chuckles at Dean's dubious expression. "I was a warrior, Dean. In every sense of the word. I led a garrison of hundreds. I was intimately familiar with every fighting style of every culture that has ever existed."

"Even Klingon?" Dean asks after a beat.

Cas smirks. "If you can find me a Bat'leth -"

"I'm pretty sure Charlie has one."

Shaking his head in amusement, Cas lays one hand over the sword at his waist. "Assuming you approve…I understand there is a den of ghouls three states over that need taking care of?"

Dean still looks slightly overwhelmed as he stares at Cas, as though noticing him for the first time. "Yeah," he says after a very long silence, shoving his hands in his pockets. "It's cool. Let's go. Daylight's burning."

"You know, I think I'm going to sit this one out," Sam says casually, pulling out a chair. "I think you two have got this, and I'd like to try and dig up some information on that sword."

To Cas's surprise, Dean doesn't object, merely shrugs. "Fine. Just you and me, Cas. Meet you at the car." He turns and strides out of the library. Cas begins to follow, but Sam grabs at his arm.

"He was totally hiding a boner just then," Sam says, determinedly looking everywhere but at Cas. "Make the most of this trip, all right?"

Cas supposed it was only fair that he be suspended in astonishment this morning, as well.