The Sharingan.

Shin: "Mmphhh!!"

In the next moment, Shin's body was immediately devoured. He wasn't going to waste time with Shin as the latter would've just kept making empty threats and any information he wanted to know would be gained from his memories.

[Ding]

[Hosts body can now assimilate foreign DNA much easier without a chance of rejection. The host's body and soul have been strengthened. The host's chakra reserve has been greatly increased. 60 points gained. Sharingan gained.]

Tendo suddenly felt a slight burning sensation in his eyes and he could feel his body being changed drastically. He could feel the basic triple tomoe sharingan manifest in his eyes and then he felt several more being "added" onto that. The power gained from each added stack was doubling the effectiveness of his Sharingan with each stack as a whole, increasing its power drastically. On Shin's body, they were about 25 Sharingan's scattered throughout it. So that meant that Tendo's full-powered three tomoe sharingan had 25 times the power of any Sharingan out there. {A/N: I'm guessing this is one of those times that you might need a better explanation fellas. Feel free to ask about what you don't understand.}

Shin's body traits were already completely absorbed and about a few minutes later, Tendo finally awakened his new eyes. Opening them, he felt like he could see the world even clearer than before. Tendo could analyze things even deeper than what his mutated byakugan allowed him too. He theorized that at max power it wouldn't be surprising if he could see down to the atomic level.

The first thing that Tendo noticed was that he wasn't always seeing three hundred plus kilometers in a 360° radius at all times anymore. That was always an ability that slightly annoyed him as it quickly got old seeing "hidden nightly interactions" that one was not supposed to see as a result. But, that didn't mean he lost the ability to do so, he just gained much more control over it and could activate it at will. His 360° vision was still active though as that was one of the main abilities of the Byakugan.

Tendo didn't know the exact limits of this version of his sharingan yet and he didn't want to wait too long to test it so he quickly began enacting his next set of objectives. He outstretched his right hand and a giant black mist like creature appeared, immediately going through the entire base, absorbing the bodies of all the "clones" of shin that had Sharingan's implanted in them too. Although these Sharingan's didn't provide as much of a boost as the real thing because they were artificial, they were still relative in power so Tendo happily absorbed them.

Of course, most of the clones were still alive and actually hid because they didn't fight Tendo initially but ran when they saw his power. Tendo had killed about 500 clones when he got into the hideout at first. He averaged that they had to be about 1500 clones left at least so he got to work finding them. In due time, they were quickly taken care of too. The most interesting thing that Tendo encountered was the awakening of the Mangekyo Sharingan by one of the clones. The clone was one of the last ones to be absorbed as he watched all his brothers go through the terrible fate of being eaten by that otherworldly black snake. Immense hatred for Tendo took over his heart as he decided to draw a giant shuriken and rushed the monster in front of him, hoping that he could at least permanently wound Tendo before he died. The Mangekyo Sharingan awakened and Tendo felt the fluctuation in chakra, a surprised look appearing on his face when he saw it appear.

Tendo: 'I didn't imagine that he would awaken that here. If I had waited until Itachi was killed, all of them would have awakened their mangekyo sharingans at that time but it wasn't worth it. I would have gained the same power anyways. But now that I can absorb his Mangekyo, I wonder if his abilities will just be added onto my own? Well, he's getting closer so I might as well test that theory out.'

The clone had just arrived in front of the seemingly unfocused Tendo, using all of his strength to push the blade towards Tendo's eyes in hopes of destroying it as he knew they were important to Tendo. While Tendo already noticed him coming and wasn't planning to spare him, he could applaud his determination in such a dire situation. It reminded him of how powerless he was when he was life and family was being taken advantage of in the past. With one downwards swipe of his hand as his fingers were lined with natural energy, he made a makeshift sword that immediately cut the clone in half on impact. Tendo absorbed him and went back into his thoughts, wondering what would be the result of his harvest. The number of points he was expecting to gain would be incredible.

[Ding]

[Host's body, soul, and chakra strength have been strengthened significantly. Hosts chakra reserve increased drastically. The host has absorbed a Mangekyo Sharingan but its abilities wouldn't be accessible until the host has naturally awakened his own. It is recommended that the host should sit down and close his eyes as fusing that many Sharingan's together is not an easy task. Should you fail, there is no guarantee that you would be able to see again.] {A/N: As fucking OP as this sounds, the initial chakra drain will be drastic, making using its abilities without constant training a detriment. But it's not a nerf as this 'weakness' will be overcome soon enough. Look forward to his Mangekyo abilities though...]

[2000 clones killed, 40000 points gained.] {A/N: Each clone was 20 points. 20 times 2000= 40,000.}

Tendo agreed with the system as he could feel an immense amount of pain in his eyes. Before sitting down though, he outstretched his hands into the snake form once again and found Orochimaru's stash which had about 30 pairs of sharingan in there. By absorbing them, the pain increased again but he didn't mind it as he knew such gains couldn't come without any pain. He walked around the hideout and found a chair within, unbeknownst to him at the time as he had his focus elsewhere, the laboratory that contained Suigetsu. Sitting down, Tendo braced back and closed his eyes, immediately beginning his absorption process.

[One month later, in the Village Hidden in the Stone]

In the clear blue skies of Iwagakure, above a massive stone structure that was eclipsing every other building in the village, a short, big-nosed man could be seen floating there with a scroll in his hands.

Onoki: 'We allowed this boy to do what he wanted for way too long. At his current strength and due to his past actions, I doubt he would want to work under the banner of any village so recruiting him would be out of the question. Now, the Hokage wants to form an alliance to take him down as even the toad sage was defeated! It would have been great if she had been defeated too but she didn't say anything about that. They're probably hiding something. Tch! I'll have to think about it and I'm sure the other villages will do the same. Times are changing once again and if another war broke out....'