The Man Known as Abyss

Sometime after the leaf village began it's mission to purge the land of monsters corrupted by tailed beast chakra, they came across a man known as Abyss.

The origins of Abyss are unknown, it is speculated that he may have originated from Oto no Kuni, as a failed experiment, this of course is just speculation.

What is known is that Abyss was a truly talented and powerful shinobi who had absorbed a great deal of tailed beast chakra and was able to manipulate and control those infected by this chakra. Abyss was easily a S ranked shinobi, whose powers probably far exceeded that of any Jonin. While his Taijutsu skills were astounding, his true abilities seemed to be in his puppet mastery.

Idaku and Shinn had departed on a mission to the land of grass, due to reports of it not being attacked by the fiends. After extensive searching they found a source of corrupted chakra within a building near the outskirts of town. They infiltrated the building and after several moments of snooping around were attacked by numerous puppets. The two fought vigilantly but were quickly being overwhelmed. Shinn being in charge of the mission ordered Idaku to retreat, which he did after much reluctance. Utilizing the last of his abilities Shinn held Abyss in place until Idaku could escape, and then he was slain. Fortunately Shinn had been wearing a wire and so the leaf village heard all that transpired between the three as it happened. This of course giving everyone knowledge of the demon. One of the important facts obtained was that Abyss had strong similarities to Pain and Kabuto.

Three months after Shinn's death, Abyss initiated an attack on the leaf village. While other shinobi were busy holding off his forces Senko bypassed them and attack Abyss directly. The battle that ensued could only be described as epic. And while it did appear Senko had the upper hand, Abyss continuously pulled out one trick after another, going so far as to summon undead puppets of legendary shinobi such as Itachi, the Third Hokage, and even Orochimaru. After a long fight, Senko managed to pull off a powerful summoning technique that brought about Ryujin the dragon god. Ryujin's ability to manipulate water on a massive scale allowed for him to destroy numerous puppets, but he was ultimately defeated by Abyss' powerful corrupted chakra. In a last ditch effort Senko and Ryujin merged, causing Senko to exceed physical human limits and utterly destroy Abyss's remaining puppets and do serious damage to Abyss. Realizing that he could be defeated, Abyss pinned Senko to the ground with a gravity manipulation jutsu, and then dropped a mountain on him, effectively killing him. Severely weaken by this jutsu and his fight with Senko, Abyss continued his assault on the leaf.

He would then engage a high level Jonin known as Taku, the two fought relentlessly for hour, and it was clear that Abyss was going to win. Yet last moment Idaku and a revived Shinn joined the fight. The three of them effectively teamed up and held Abyss at bay. Idaku and Taku distracting him while Shinn performed a powerful jutsu that destabilized Abyss' atomic structure causing him to exploded into dust.

While it is unclear why Abyss wanted the tailed beast, it is safe to assume that he was manufactured and that there was most likely a greater master mind manipulating him.