Or, Uchiha Madara's Terrible, Horrible, No Good, Very Bad Day
Time travel? Perhaps.
Uchiha Madara was annoyed.
It was certainly horrible looking, but it was far too small, had the chakra aura of a common rock, and didn't have even a single tail. It was also wearing a robe.
He reminded himself to go back and kill the old coot with the odd markings (clan tattoos, perhaps?) on his cheeks. He had thought there was an odd undercurrent of glee in the oldster's voice when he had told Madara about the location of a new, and never-before-seen type of biju.
"You're not one of the Tailed Beasts, are you?" growled Madara.
"Not at all," the monster answered in a soft, whispery voice. "Might I inquire as to whom I am addressing?"
Madara felt vaguely uncomfortable. The monster was leaning forward and appeared to be closely inspecting his face.
"I am Uchiha Madara, a god among men, master of ninjas and biju, not to mention snappy dresser. What are you, beast? Flesh, fish, or fowl, demon or ogre? For I have never seen anything quite like you."
"You have beautiful eyes, Uchiha Madara" was the monster's non-sequitur.
Madara blinked. He noticed again the numerous…objects woven into the monster's robe. He was definitely going to have to kill the old man in a particularly atrocious manner.
Ok, make-them-piss-themselves-aura time.
"Again - what are you, creature? Don't try my patience any further, or I shall reduce you to a grease spot. I have bent the Nine-Tails itself to my will - I could crush you like an ant."
The creature didn't even blink its black, bottomless eyes. Instead it grinned, showing what struck Madara as rather more teeth than should have fit in even that commodious mouth. For the first time since his fight with the First, Madara felt - what was that word again? Nervous.
"I am…"
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The landscape was white, featureless, like an empty stage setting. In the black, starless sky a blood-red moon shone. It traced in crimson the outlines of a hideous black creature, nailed with many sharp, metallic spikes to a huge cross. [1]
Madara Uchiha, his equilibrium restored, sneered.
"You are powerful, beast - I'll give you that. But now you are within my genjutsu, and you will die a million times before I…"
Madara blinked. The shape on the cross looked different, as if it had somehow shrunk and grown darker, harder to see. But that was impossible - the only reality in this realm was defined by his will. Even as he looked, the black shape seemed to somehow drain into the cross, like water seeping away, and disappeared. Madara stared, but the monster had vanished - and he had not willed it.
A huge, malformed paw then closed around his head with irresistible force from behind. And the whisper in his ear was the last thing Madara Uchiha would ever hear…
"I am Chun the Unavoidable."
[1] No, I don't know if Madara has the Tsukuyomi, but given his frankly absurd power level, I wouldn't be surprised…