Let’s bring destruction to this world. If you want to stop me, then show me if you can!Yuuki's code of conduct.
Yuuki Kagurazaka, formerly the Free Guild's Grand Master, is one of the main antagonists of Tensei Shitara Slime datta ken. A twisted genius with massive influence, he easily manipulated countless people whom he encountered the moment he arrived in this world.
He has pleasing features with black hair and eyes. Although his age is in the mid-20s, his features remain that of a high school student. This is most likely due to some kind of curse similar in nature to Hinata's.
At first glance, Yuuki is a bright and optimistic individual. However, his easy and good-hearted nature is but a mere facade for his destructive and suicidal personality. Given that he is a genius, Yuuki always stays one step ahead. Therefore, he is uneasy with the existence of unknown factors, such as Rimuru, that could endanger his future plans. Ever since arriving into a new world where powerful enemies existed, he rejoiced at the fact that this was a world without boredom, one where he could give form to his warped existence: Ruthless, insane, calculative, and sadistic. He does not view humans as people but as bugs. For those who proved useful, he would think of them as pawns or pieces of the chessboard.
For his desire to come into fruition, Yuuki had established his position as the Grand Master of the Free Guild and crafted himself the reputation of a caring and wise superior to others. Gaining the recognition, respect, trust, and admiration by performing grand feats, such as slaying dragons with ease, he instills the image of a powerful leader that others would look up and depend on. Everything that he has done, ranging from planting parasites into the minds of friends, manipulating unsuspecting people, and causing the death of innocents, is all for the sake of his goals. Nothing he does are for the benefit of others, showing the absence of his sense of humanity, justice, and empathy. He holds no feelings for his followers, nor does he feel anything toward their deaths.
Since his childhood, Yuuki was a genius. When he was still in the former world, he had harbored dangerous dreams of destroying the boring everyday life. It was just that, in the former world, he hadn't held a fascination for the world's destruction.
Earning money wasn't a problem for him. If he wished for it, he could obtain it, but for him, there was already nothing he really wanted. When Yuuki had just become an elementary school student, his parents were killed in an accident. His parents hadn't made a mistake; they collided head-on with a truck whose driver had fallen asleep at the wheel and died instantly. This left Yuuki, who was sleeping in the rear seat, as the sole survivor.
This event caused Yuuki to believe that the world was utterly unreasonable and that he was hopelessly powerless to do anything. The idea of revenge against such an unreasonable world had become rather amusing to him, but he quickly gave up on any further thoughts. He was a genius that could accomplish anything that he wanted. Had he seriously wished for it, it might really have been possible to turn the destruction of the world into reality.
He honestly believed that the world was boring. It is possible that his thirst for destruction was suppressed by that thought. For him to cross over into a new world filled with different possibilities was his good fortune and the misfortune for the fate of the inhabitants of the new world.
Yuuki sees Rimuru as a thorn in his side, an unknown factor. He was surprised by Rimuru's rapid growth and regrets not killing Rimuru back when they first met. Ultimately, Yuuki died at the end of the series when Rimuru digested him.
When he came to this world, he claimed that he did not acquire any Unique Skills or abilities, only that his physical abilities grew abnormally fast. Evidently, it was all false.
By using Memory Orbs, Yuuki could recreate a dead person by implanting their memories. Furthermore, it was possible to grant them energy and skills. However, as the soul is not present, the result can't be called a living being. This was done with Damrada and Tatsuya Kondou, both of which retained their abilities. According to Velda, they gained a power comparable to 10 awakened Demon Lords, but that was soon debunked by Veldora who stated that their EP is no more than half of what Velda acclaimed i.e., 5,000,000(+).
- Snake Sword: Legend Grade weapon that Yuuki possesses. This weapon is flexible, though it was still usable as a knife. It can extend and be used as a whip because it can change its shape freely. Furthermore, it has the ability to absorb a fixed amount of damage. Until it reaches its limit, the sword can nullify all attacks it receives. However, once its capacity is reached it can't be used until it recycles in one week. It was destroyed by Milim.
- Veldanava Sword: A Genesis Class sword created from Veldanava's corpse. It allows Yuuki to use energy beyond his own limit. In the final battle against Rimuru, he injected most of his powerful skills into it and let Velda control and maintain them while he himself stood busy against Rimuru. Such an action was a double-edged sword because not only did it allow him to use powers beyond his limits, but it also meant that he would lose all of them if he lost the sword.