Kakuzu finally stopped running, feeling that the sand ninjas didn't pursue him, and sighed in relief.
This mission was a veritable disaster of bijuu proportion and he still had a hard time coming to grips with how easily and quickly he was forced to retreat.
'There is no way these were genins.' Kakuzu wearily thought, unable to even be mad at his loss of four hearts. He was too tired to even contemplate getting angry.
Not physically. His tiredness was of the mental kind. It was weariness at having his preconceived notions of how the world worked forcefully broken. Kakuzu was a realist and knew he was not on top of the world. There were plenty of stronger fishes in the pond, so to speak. He, however, took pride in his strength and fully believed he would be solidly placed among the top twenty ninjas in the world.
Getting his stuffing beaten out of him by brats who were just entering their teenage years, even if they had Sasori's help and the advantage of an ambush on their side, was a heavy blow to Kakuzu's pride and worldview.
Kakuzu could take the loss of Hidan. The welp was not important. But four of his hearts! It will take him ages to replenish those. Yes, hearts were readily available resources if one knew where to look... But Kakuzu needed quality rather than quantity and there were not that many powerful ninjas with strong affinities across the world, much less many opportunities to get their hearts.
The only bright spot on this whole clusterfuck was that the heart of the Second Hokage was undamaged, still beating in his chest. Kakuzu was aware he would be unable to get a better quality water heart... ever. That's why he seldom took it out of his body.
"I see that you took a beating." A dark scratchy voice suddenly resounded in front of Kakuzu, making him alert and raising his guard up in an instant.
Zetsu suddenly emerged from the ground in front of Kakuzu, causing the old bounty hunter to relax again at the sight of his organization's spy.
"Zetsu. What are you doing here?" He gruffly asked, not paying him much attention as he was too focused on stitching his wounds shut.
"I was tasked with observing this mission." Zetsu indifferently replied, his tone holding a hint of amusement at Kakuzu's sorry state.
"Of course you were." Kakuzu grumbled. Part of him was irritated that his failure was witnessed by somebody but part of him was glad because it meant he would not be held fully accountable for it once Zetsu testified about the battle.
Nobody, not even the leader, could blame him for retreating when outnumbered by three dangerous individuals.
Plus... it was mostly Hidan's fault for rushing in. Kakuzu reckoned there would be no digging that dipshit up and putting him back together this time.
"Well, I should return to my stalking assignment. It would be very problematic if I lose track of our target." Zetsu suddenly said after a minute of silence between him and Kakuzu, getting only a dismissive grunt in return.
It didn't bother him. Akatsuki was not some kind of dysfunctional family. The sheer thought of that was ridiculous beyond belief. They were coworkers and mercenaries that could barely stomach themselves at the best of times.
Kakuzu barely registered Zetsu about to pass by him as he mentally grumbled and tried to remember the best elemental users from his bounty lists. He will have to spend the next two years on the hunt for new quality hearts and it was already making him irritated when he thought about the effort he will have to exert.
'And Pein will definitely expect me to continue my hunt for bounties.' Kakuzu thought in irritation. He often regretted joining Akatsuki. Not that he had much of a choice. When someone like Pain appears before you and gives you a clear choice between joining and death, the answer is obvious.
Kakuzu might have tried to pull Orochimaru on Akatsuki by now if they didn't provide him with so many financial benefits, to be honest.
As he was lost in his mind, his instinct suddenly flared in danger, jolting him awake from his reverie but... he was too late.
A sharp pain abruptly rushed through his chest as Kakuzu involuntarily spat blood before inclining his head downward in pained confusion only to notice a black arm sticking out of his chest, straight through his last remaining heart.
Horror instantly engulfed his mind as he realized what that meant for his 'immortal' self.
"Z-Z-Zet...su!" He gritted out in disbelief and anger, realizing who was responsible for his upcoming demise. "Wh-y?" He gurgled through the blood that tried to rush out of his throat.
"Because your continued survival is in the way of my mother's wishes." Zetsu calmly said, not worried about revealing it to Kakuzu. The man would die here and he had no way to relay this information to anyone. Zetsu knew. He had extensive knowledge of all Akatsuki members. He probably knew them more than they knew themselves at this point.
Hearing that, Kakuzu's eyes widened as he understood. He understood that Zetsu was not as loyal to Akatsuki as he portrayed but... 'He is one of the initial members!' Kakuzu thought in dismay. But that could only mean, 'We... we are all just puppets in his schemes, aren't we?' The dying man realized in painful astonishment. Zetsu was supposed to be the weakest of them but this...
Akatsuki suddenly seemed much darker than it outwardly appeared and Kakuzu cursed himself for getting caught in its web.
"It is funny, you know?" Zetsu's voice resounded from behind Kakuzu, laced with light amusement at the disbelief of his soon-to-be-ex colleague, "I am the weakest member of Akatsuki. Just a spy. Someone not worth being cautious of because I could never pose a threat to any of you. Thanks to that, most of you like to completely disregard my presence. You didn't notice anything was wrong until my hand was already about to penetrate your back." Zetsu let out a cold chuckle. "S-rank ninjas indeed. Oh, how the mighty have fallen."
That was the last thing Kakuzu heard as his consciousness failed him, casting him forever into the oblivion of death.
Zetsu looked at Kakuzu's corpse that unceremoniously hit the ground and smirked, "I lied. I was never tasked with observing your mission."
Unfortunately for Kakuzu, with him still in the picture, the news of this failure would reach Pein very quickly and he would then organize a larger force to take down Sasori. This was a prime opportunity to hunt themselves a traitor, after all.
That, however, would disturb the peace of mother's friends and one of Zetsu's orders was to not cause trouble for them. Kakuzu simply had to go.
This way, Pein would not know about the outcome for a week or so before he will inevitably but correctly assume the worst after not receiving any communication from Hidan nor Kakuzu. It was not a long delay but by that time, mother's friends will be long in Konoha.
Zetsu could care less what happened to Sasori after that. The only reason why he even cared was that Sasori was escorting Rei and Tsunade.
Kaguya had no idea what kind of horror she unleashed with her casual and careless words for Zetsu would stop at nothing in order to fulfill her orders. Alas, what she meant him to do and what he perceived she meant him to do were two different things.
Not that the Rabbit Goddess could care less but the unsuspecting Akatsuki was in for a very bad time.