He would never tell Hidan, of course, but Kakuzu truly didn't want to die. He was convinced that the impossible was never really that, and if the goddamned idiot was immortal, then perhaps his god did exist.
Kakuzu didn't want to give the jackass the pleasure of knowing he was right.
Life was something constant and unchanging… like money. 700 years of it and everything still felt the same as it had at 80 – old. What difference could the afterlife make? What could it hold for him?
The closest he could ever get to heaven was pulling it further away from his partner. Nirvana was flashing violet eyes and unkempt silver locks. Paradise was made of deep scratches and uninhibited, keening noises from beneath him.
Life was, on the other hand, "I don't fuck you for your pride, you old shit. My body needed this, and Jashin shames us."
Throw in a few insults to feed the monotony of it all.
Kakuzu knows that when he's threatened, he's not in danger. "I should kill you, you bastard! Always saying my god's a farce - Lord Jashin condemns your sins!"
Those angry violet orbs… But Hidan doesn't want to kill him, though he's the only one who could.
That afterlife doesn't exist, Kakuzu knows this.
Hidan doesn't want to give him the pleasure of knowing he was right.