Yuuki Kagurazaka

"“Of course I won’t. I am definitely going to rule the world. And then everyone will live happily ever after!”"

- Yuuki

Yuuki Kagurazaka (神楽坂優樹) is a Japanese Otherworlder summoned into this world and also used to be the Grandmaster of the Free Guild. He has some connection to Shizue and thus to Rimuru. Currently, he's the Commander of the Eastern Empire's Mixed Corps, one of the four heads of the Imperial military.

Appearance
He's considered fairly handsome, with black hair and black eyes. He looks as young as a middle schooler, despite his real age being in the twenties.

Personality
Yuuki is a kind, good-natured, and hardworking person. Always bright and optimistic, Yuuki is an ideal for many adventurers for his many good deeds. However, he is also a master in manipulating others, fully willing to resort to underhanded tactics in order to achieve his goal of world domination, all to create a just world that treats everybody fairly.

Despite being manipulative for his own gains, he is very loyal to his sworn friends i.e. the Moderate Harlequin Alliance. He also treats his subordinates well and genuinely concerned with their wellbeing.

Background
A natural born genius, Yuuki was satisfied with his life on earth. He had loving parents and plenty of friends. But after an overworked truck driver fell asleep at the wheel and crashed into his parents car killing them both, he fell into despair. When the courts ruled the driver innocent, Yuuki discovered the unreasonableness and flaws of society. He initially wanted to take revenge and tear it all down but couldn't bring himself to inconvenience so many innocent people in the process. Instead, he realized that he would have to change society one step at a time by becoming a politician and gaining like minded friends and allies who would help him achieve a more fair society. But before he could even finalize his plans he was summoned to the otherworld.

Kazaream, a former demon lord on the verge of death due to his defeat at the hands of Leon Cromwell, had summoned Yuuki whose material body and spiritual body was compatible with their astral body and attempted to, with the last of their strength, lay a curse on Yuuki that would kill his mind instantly and allow them to reincarnate into his body. However, Yuuki being a genius who already understood how the world worked during the trip between worlds, had awakened his Unique Skill "Creator" and used it to make his special attribute, "Anti-Skill", letting him resist the curse. Yuuki, taking pity on Kazaream, allowed them to inhabit his body and promised to find a body for them to reincarnate into saving their life.

After letting Kazaream inhabit his body, at some point he wound up under the tutelage and guidance of Shizue Izawa alongside fellow student Hinata Sakaguchi, who were fellow countryman. There he learned about the world's language and society. Alongside his teacher, Yuuki used his knowledge of a more modern world to rework the society of adventurers into the internationally accepted Free Guild, which he was then appointed Grandmaster of. Under his leadership, monster related deaths decreased dramatically and a new system of ranking monsters based on their amount of magicules was established. These changes allowed for trade to blossom and the population to boom in areas that were previously poor and decrepit, improving the lives of many.

At some point, Yuuki encountered Mariabell Rosso who was secretly manipulating society and the economy from behind the scenes via the Council of the West, which she had complete control over. Mariabell stood as an absolute roadblock in Yuuki's goal of a fair and just society and blocked his plans off at every turn, much to Yuuki and Kazaream's annoyance. At sometime Yuuki met Damrada and crushed the dark organization in the east known as "Echidna," reforming it into the underground organization Cerberus. He appointed Vega, Misha, and Damrada as its commanders. Eventually, an opportunity to strike back at Mariabell came when she attempted to dominate him with her Unique skill, Greed. Yuuki managed to resist her domination due to his "desire" being stronger than hers and used his position to secretly influence Mariabell's mind and actions in return.

Trivia

 * Yuuki is one of the characters who had been changed the most between the Web Novel and the Light Novel. His entire character has been reworked and his motivations are completely different, to the point that his actual "role in the story" might end up a completely different one in the Light Novel compared to the Web Novel.
 * If Yuuki converts all his energy into magicules, he could rival the likes of Luminous and Leon.
 * Yuuki's English Voice Actor, Clifford Chapin, also voices Gobzo.
 * As a running gag in Slime Diaries, Yuuki was portrayed as one who's constantly trying to put feminine clothes on Rimuru.