Set some undetermined time after Aizen's defeat and Ichigo getting his powers back.
Three Vasto Lorde rip open Garganta into the space above Karakura Town, one of them a natural-formed Arrancar, and the moment Ichigo—there visiting Yuzu, who is the last of the Kurosaki family left in the world of the living—senses their reiatsu, he flash-steps into combat, already in Bankai with power roaring through his veins.
He could handle three of them—of course he could, he's Kurosaki Ichigo—but he's nonetheless glad when Yoruichi and Urahara join him, the former in Shunkō and the latter with his Zanpakutō released. It should be an easy fight, and it almost is.
Until they forget that Arrancar—so used to dealing with Nel and her fracción—are just as ruthless as ordinary Hollows, and Yoruichi takes a Cero to the torso just as she finishes the second Vasto Lorde. The blast punches straight through her chest, searing away most of her flesh as it burns a hole through the Vasto Lorde as well.
"Yoruichi!" two voices scream.
Ichigo flash-steps to catch her, but Urahara is already there – he moves so quickly that Ichigo is not entirely sure if he bothered to pass through the intervening space. Acting on instinct—his conscious mind is not quite there, still reeling in shock—with his Hollow mask already bleeding through his skin, Ichigo is half a second away from annihilating the Arrancar when something clamps down on his forearm.
His fist is halfway to his attacker's head before he realises it is Urahara's hand holding him back. No words need to be said; one look in the man's eyes is all Ichigo needs before he flash-steps out of combat, leaving Urahara as the Arrancar's sole opponent.
When the Hollow's Cero rips through the sky, Urahara is simply not there. He flashes across the sky, one, two, three steps every bit as fast as Yoruichi on a good day – sure, Ichigo's seen faster, gone faster, but the functioning parts of his mind are impressed regardless. The Arrancar looks around, trying to follow his movements as it hurls Bala left and right; it never hits anything but his afterimage. Urahara is untouchable.
The man reappears, briefly, right behind the Arrancar, and for a moment Ichigo is sure everything is over – until Urahara simply taps it on the shoulder. It spins around, clawed hands ripping through the air, and Urahara punches it in the face. Hard. The sort of punch that can only be called earth-shaking. The only reason the Arrancar does not go flying is that Urahara has a grip on one of its arms, holding it in place.
Then he punches it again.
And again.
And again.
Fist impacts hierro like a smith hammering steel; Urahara is, quite literally, rearranging the Arrancar's face. There are visible dents, and when Ichigo is sure that the next punch will kill, it never comes. Instead, Urahara changes the location of his strike, and takes the Arrancar's arm off at the shoulder.
It's not a clean amputation; Urahara wrenches the arm he was holding toward him as he punches forward faster than the speed of sound, straight into the ball-and-socket of the shoulder joint. It tears off with a vicious crack, and before the Arrancar can even start screaming, Urahara takes a step back and spins, the detached limb held in both hands like a baseball bat, and smashes the Hollow into the earth with its own arm.
It is the single most brutal act Ichigo has ever seen, and it is in that moment that he realises he never, ever wants to make Urahara angry.
The man himself descends to the ground, each step slow and measured, and Ichigo wonders if this is what he might look like to his enemies, some dark and vengeful god. Urahara walks over to where he had plunged his released zanpakuto into the earth, and draws the blade out, not even paying attention to the slowly-rising Arrancar. His other hand is still holding the Hollow's arm.
Benihime glints in the sunlight, and Ichigo is not entirely sure if it's a trick of the light when crimson seems to ripple across her blade. It is the colour of blood, of anger, of violence; just like the shield that blooms before Urahara as he turns, taking the Arrancar's Cero almost point-blank. When the dust clears, Urahara is entirely unmoved; he stands straight and tall like the blade of his sword, and he is smiling.
It is not a smile Ichigo has ever seen on his face before. It is not a smile Ichigo ever wants to see on his face again. It is not amused, not laughing, not smug or satisfied. It is death. Urahara is smiling in the same way a skull might.
He takes a step forward, then another, moving with the casual inevitability of a man who knows exactly how long you have left to live, batting Bala aside with the Arrancar's own amputated arm, and starts to speak.
"Have you ever wondered, Ichigo, what a person's Bankai says about their soul?" With every word, Urahara's reiatsu grows. "Your Zanpakutō spirit is the shadow of your soul. It is a reflection of all the secret parts of your subconscious. What, then, does it mean—on the metaphysical level—that your soul has releases – releases that translate directly to power? What exactly is Shikai? Or Bankai?"
The Arrancar hurls itself forward, claws outstretched, and Urahara backhands it across the face with the limb he carries, smashing it back fifty metres.
"The answer is simple: they are understanding. Learning the name of your Zanpakutō, gaining Shikai: that is self-acceptance. It is a burden, one every Shinigami must bear willingly. To gaze into your soul and not shy away—to not be afraid when it gazes back—is not easy. Men have been driven mad by far lesser truths than that."
In the distance, the Arrancar is slowly rising once again.
"Then, of course, there is Bankai. If Shikai is self-acceptance, then Bankai is self-enlightenment. To gain Bankai, you must conquer all the hidden parts of your soul. You must have dominion over everything you are – over everything you could ever possibly be. A shinigami with Bankai is a being at complete harmony with the whole of their being: ying-yang given form."
Another Cero is charged and fired; Urahara splits it apart with a single slash as Benihime sings.
"Which leads us to another question: what does a person's Zanpakutō say about them? What can you discern about a shinigami from the nature of their Shikai, or from their Bankai? What can they discern about themselves? The answers, naturally, differ from shinigami to shinigami. But let me tell you about mine."
Benihime sings a different chord, and Urahara hurls a bloody net over the Arrancar, trapping it where it stands.
"My Zanpakutō is female. That, straight away, tells me something: that the silent depths of my soul—the parts that lives below the surface—are so unfathomably alien to the rest of my being that they must express themselves as a different gender. My Zanpakutō's name is Benihime – another clue. Crimson: blood, anger, rage, violence, lust, love. Princess: arrogant, aristocratic, beautiful, ruler, prize."
He circles the Arrancar with slow, languid steps, and it takes Ichigo a moment to realise Urahara's grace has always reminded him of royalty.
"Combine their associations together, and consider what you get. Bloody ruler. Anger and arrogance. A lusted-after prize. Violent beauty. My Zanpakutō's name is an expression of everything she is. Everything she will always be. Benihime is the name my subconscious has taken for its own – and there are few things that can tell you more about something than what it calls itself."
His reiatsu is still building, like a gathering storm.
"Consider also her release command: awaken. To bring out the physical manifestation of my self-acceptance, I must awaken it. Zanpakutō are sentient – so, to awaken her, she must first be sleeping. Ignoring the world around her. Why? Is the shadow of my soul so arrogant that she spends most of the time dismissing existence, taking interest in only the most fascinating of things? Or is she simply lazy? I can tell you now that she is both. Which means, of course, that I, too, am both."
The Arrancar struggles wildly, but this is a net that once, briefly, held Aizen – its struggles serve it no more than a fly's might.
"But we can go deeper. What happens when she wakes up? She sings, she cuts, she shields, she spurns, and she binds, all with bloody crimson. Benihime is a princess amongst peasants – she kills anyone who gets in her way, ignores those who make to kill her, and, if she so desires, she takes."
Urahara laughs, and there is violence in it.
"As above, so below. When I accept myself, this is what I learn: that I am a killer, that I am arrogant, that I take. I hide it well, of course – that is why my Zanpakutō's release command is awaken. Most of the time, my baser nature sleeps.
But not today. Not now."
He takes a step back, reiatsu thickening, and Ichigo just knows what is coming.
"My Shikai tells me that I take. But do you know what my Bankai tells me? It tells me that I consume."
There is a pause, like the space between lightning and thunder.
"Ban. KAI."
Urahara's reiatsu detonates like a supernova.
"Jisankyomu Benihime."
The sword in Urahara's hand is terrifying. Sharp as starlight, and twice the length of Urahara's forearm, Benihime's blade is a rippling expanse of ruddy steel. Lines of crimson spiral from the tip to the guard, thickening as the blade does until the hilt itself seems formed from blood. She is a blade forged from agony, from violence, from death.
Her appearance, however, is not what sends that little shudder of fear down Ichigo's spine.
Rather, it is the corrosion eating away at his Reiryoku, scouring him like he's bathing in acid, that makes his very being cry out that something is wrong. His soul is being violated – it is being consumed. For the first few seconds, it is everything Ichigo can do not to scream.
The Arrancar is not so lucky.
It is howling, reiatsu flickering, its very core being eaten away faster and faster as Urahara steps closer, until Benihime's tip rests at the crook of its neck through a gap in the net. The flesh beneath the blade is peeling away, sloughing off in strips and collapsing into reishi.
"Hello," he says, each syllable like a razor in Ichigo's ears. "My name is Urahara Kisuke. You killed my best friend. Prepare to die."
Urahara lunges forward, and Benihime impales herself right through the Arrancar's spine. Then he releases her hilt and walks toward where Yoruichi's body lies.
Behind him, the Arrancar is no longer screaming. It no longer has vocal cords.
As Ichigo flash-steps away—the Hollow within howling getawayescapefleemonster—to give Urahara time alone to mourn, he sees something manifest behind him.
There, crouching next to Urahara as he kneels over Yoruichi, is a woman, draping her claw-nailed hands over his shoulders. She is pale as bone and beautiful as blood, her dress formed from roses and studded with thorns—Urahara does not seem to notice the way they dig into his neck—and on her forehead rests a crown that perfectly matches the sword still embedded in the slowly-melting Arrancar's throat.
That is not what catches his eye, however.
No, he is drawn to the hole through her breast; perfectly black and perfectly circular, it is something Ichigo knows well.
Urahara's Zanpakutō spirit has a Hollow hole, right where her heart should be.
Jisankyomu Benihime (持参虚無紅姫): Oblivion-Bringing Crimson Princess (literal translation 'bringing nothingness red princess') is Urahara's Bankai. When active, it consumes the Reiryoku of any being—spiritual entity or ordinary human—within a certain radius, and then uses it to amplify his Shikai abilities. The closer you are to Benihime's blade, the faster the drain.
For reference, I'm not saying that Urahara has an inner Hollow. The reasons Benihime chooses to manifest with a Hollow hole should be fairly obvious, however. (If they're not, tell me, because it means I need to make things clearer).