Personality: To any passer-by, Omi may seem carefree and naive. His innocent demeanor and attitude leads some people to believe that he knows very little of the world, when in reality, he's experienced the depths of pain which many will never face. It's very true that he is a kind-natured, good-hearted young man, but he has a lot of guilt and torment resting on his shoulders.
When he is greatly upset by something, it doesn't take very long for Omi to break down. He has little control over his emotions when something really wreaks at his mind and heart, but he doesn't seem to be ashamed by it. He believes that everyone deserves to be treated fairly, that everyone deserves a second chance, even if they have done wrong. His biggest problem is that he doesn't seem to take his own creed to heart. He understands that what he has done in the past was for the greater good, but it still torments him. He can't seem to let the anguish that accompanies his past fade away: perhaps something or someone at Haurvatat may be able to change that.
History: Omi was born and raised in Japan. He started his life as Mamoru, the youngest son in the household of Reiji Takatori. Reiji was a very influential man in politics who had two older sons, Hirofumi and Masafumi. When Omi was very young, his mother committed suicide. At the age of seven, he was kidnapped. His kidnappers made the demand for his father to pay a ransom for Omi's return; however, they told him that his father refused to pay it. Soon after the phone call and telling him that his own father wouldn't pay any sum of money for him to be returned, he was rescued by his uncle, Shuichi Takatori. Omi did not realize who had saved him at the time.
Sometime after Omi was saved, he suffered from amnesia. When he was a teenager, he was assigned to be the head of an assassin group that dealt with the crooks and evil-doers in Tokyo. Most of these criminals had some tie with the Takatori family. While also leading this group, known as Weiss, he and his teammates worked at a flower-shop as their cover. While working as a florist by day and assassin by night, Omi also attended high school.
While working on a case that dealt with a kidnapped child, Omi's memory slowly returned to him in bits and pieces via intense flashbacks. He realized that it was the leader of Kritiker (the organization that gave Weiss orders), that had saved him: this man's code-name was Persia. Furthermore, there were more pieces of Omi's life that had yet to fall in place.
When Weiss was given orders to kill Hirofumi, Reiji's oldest son, Hirofumi became overwhelmed with emotion and asked Omi if he was someone named Mamoru. Omi then researched who Mamoru was and found out that he was the long lost son of Reiji Takatori. After he discovered this he refused to kill the man he thought of as his brother, until he was tortured by Hirofumi for information about Weiss. Sometime around these events, Omi also discovered that Persia was actually his uncle, the brother of Reiji.
When discussing the romantics of Omi's life, there was one girl in particular named Ouka Sakaki that was very fond of him. She would visit the flower-shop very often, buying flowers specifically for Omi. She convinced him to attend a party with her, as her date, so that she could introduce him to her father. A few days after the party, Ouka learned from a bodyguard of her father that Omi was her brother. After this, she found it very hard to tell him of the news. One night while Ouka told Omi that he was her brother, they decided that they could still love each other, but as a brother and sister would. Omi finally had one person in his life that he truly loved and thought of as family that he could relate to, but she was murdered by another bodyguard of Reiji. Omi was heartbroken and distraught.
To sum everything up, Omi was oblivious to that fact that Persia was his real father, not Reiji. His mother and Shuichi (Persia) had been in love, but she had been forced to marry Reiji. Omi discovered Persia dying from Reiji's bullet (Persia had found out that Omi was his son only moments before he was shot), thus losing yet another family member. Persia, however, did not tell Omi that he was his father before he died. Sometime after Persia's death, Reiji was also killed. In result of this, Omi lost absolutely everyone that he considered a family member.
Even after having to kill his family members and seeing his family members die, Omi still headed Weiss and continued his role as an assassin. He was left believing that he had fallen in love with his sister, and that his father was a scheming, evil man who killed his uncle.