Bleach obviously isn't mine, though I will claim the name of Urahara's bankai, only because it hasn't been seen in the anime yet. If I did own bleach, Kon and Kurotsuchi Mayuri-taicho wouldn't exist.

He'd meant what he'd told Abarai-kun about his bankai that it was of no use in Sado-kun's training. What he wasn't about to mention, was the reasons behind that pronouncement.

Benihime, his lovely, glorious crimson princess, was a blood based zanpakto, like that adorable Hitsugaya-kun had an ice based sword, and Kurosaki-kun's was speed based. As with all zanpakto, the strengths and abilities of the shikai release, were enhanced and magnified during bankai. That was all fine and dandy when you had a zanpakto like Abarai-kun's, but with his?

You never would have guessed it from her name or appearance, but when Benihime went after an enemy, they went down. It was just that simple. Despite having worked with her for several centuries before attaining bankai, even he hadn't completely grasped how extremely ruthless his small, delicate, lovely zanpakto was. It wasn't until she granted him bankai and he realized Kirikizu Benihime that Urahara Kisuke discovered Benihime's true nature.

A simple cut. It didn't need to be in a vital spot, barely even needed to draw blood. That was all Kirikizu Benihime needed to kill. Her power could open the wound, widen it, and deepen it, until in some cases, until it cut the enemy in two. She could bleed out every wound an enemy suffered, even if the enemy could heal itself. He'd seen enemies end up cut in pieces from the lightest scratches, and seen simple bruises ripping off limbs. Kirikizu Benihime's power was in turning her opponent's own blood against him.

Yoruichi had never seen it happen. And if Urahara had anything to do about it, she wouldn't. She had enough nightmares about her time in the Special Forces with out adding new ones from the sights of what remained after Kirikizu Benihime finished with an enemy. She didn't deserve the sleepless nights he'd had ever since he'd started training his bankai.

For his crimson princess was no delicate flower on the battlefield. How could she be, when she's made of blood?

Owari

Kirikizu—cut, as in wound.

I'm just guessing with what Ichigo's and Urahara's zanpakto are based on. I guessed speed for Ichigo, because the Tensa Zangetsu is all about speed and blood for Benihime because she looks like a lancet which was used to bleed people, plus, the shield she's got is called a "blood mist" shield. Check the manga, vol 8 if you don't believe me.

About Benihime's appearance, I mean like how Zangetsu has that long hair, coat and shades. Remember when we se Yoruichi all gussied up in Soi Fong's memory? Hime means princess, so similar outfit, but in various shades of red with pale skin, red eyes, and black hair.