Soul Reapers Work For Death: Book 1, World of Death

A Dark Instinct.

Some clearing up to do before this chappie goes further. When Hollow Ichigo says he's Zangetsu, he's actually exactly right. Ichigo's hollow form is in fact the spirit of his sword Zangetsu, his true Zanpakuto that was a result of his soul reaper powers combining with the hollow known as White who attacked Ichigo's mother years ago and lay dormant within his mother and was then passed to him. The old man who pretended to be Zangetsu, is actually a manifestation of the Quincy powers Ichigo inherited from his mother. White, now being Zangetsu, was created by Aizen as an experimentation of hollowfying Soul Reapers.

"HAHAHAHAHA!! COME ON!!! YOU CAN DO BETTER THEN THAT!!" White Ichigo.. right now known as Zangetsu swung his massive blade at Tsubaki in wild unpredictable motions, laughing his head off as he dashed at her with incredible speed.

Tsubaki flipped away, using some pretty powerful speed of her own to avoid Zangetsu's strikes. "Th-this doesn't make sense! A-are you Ichigo's brother or something!?"

"Are ya kidding me!?" said Zangetsu raising an eyebrow, his psychotic eyes widening. "Ya really don't have a clue what kind of power Ichigo possesses do ya? I ain't his brother, this beautiful mug's got another reason for looking so much like my landlord!"

"What would be that reason?" Tsubaki asked, trying to sound as diplomatic as possible.

"OH WHAT THE HELL!!?" said Zangetsu with another laugh. "You're so darn soft!! Not an ounce of Instinct in ya! You fight so good, yet without an ounce of instinct, you're going get hacked up like cute little bunny in a blender!!"

Tsubaki dodged another set of slashes from Zangetsu. Zangetsu grinned however and used the cloth on the hilt of his blade and spun the sword around like a buz saw before throwing it directly at Tsubaki. The blade sliced passed Tsubaki's leg, cutting a bloody gash as she attempted to dodge..

"Woops!! I missed.. NOT!!" Zangetsu pulled back on the cloth of the sword hilt, litting it spin and slice toward's Tsubaki's back. Tsubaki did a backflip over the blade and threw one of her chain scythe blades at Zangetsu.

Zangetsu flashed out of the way, laughing some more. "OH! Finally going on the attack eh!? Well well! You're gonna get your overgrown ass chucked if ya think a puny attack will do! COME ON GIRLY!! WHERE'S THAT INSTINCT!!!?"

"It's right here!" Tsubaki's scythe glowed and turned into a strange black katana that looked similar to Tensa Zangetsu.. however it's blade was thinner, it's tsuba was a light brown.. and there was no chain on the end of the hilt..

Tsubaki dashed forward with a burst of speed as the Uncanny Sword's blade became wrapped in thin tendril-like shadows.. all of a sudden, all the shadows in the ariea shot out of the ground like tenticles moving towards Zangetsu.

Zangetsu laughed again and spun like a top, using his massive blade to slash the shadows to pieces. "NOW THAT'S INSTINCT!! That sword's gotta pretty sinister feel to it girly! The spirit of that blade's feeling quite ominous!! But let me ask ya!!"

Zangetsu lunged forward and hammered his massive blade at Tsubaki who blocked it in a burst of sparks with his blade.

"Which presence feels more ominous? The thing in that sword... or the Zangetsu.. inside Ichigo's ZANGETSU!!?" Zangetsu let out another laugh as a massive pressure slammed onto the surroundings, causing Tsubaki to catch her breath as she was bashed back.

"So.." said Zangetsu. "What's gonna happen to your body when I kill ya here? Is it just gonna drop dead? Or are ya just gonna wake up it's some bad dream? Hell if I care.. cause your battle instinct really stinks!"

Zangetsu thrust his massive blade forward as  a malicious white energy with a red aura began to surround him. "Bankai.."

Tsubaki's eyes widened as White Ichigo was obscured by an explosion of white energy, emerging to reveal he was wearing an inversed color version of Ichigo's bankai coat, with a bone white Tensa Zangetsu to match.