Shibin is immoral, but not evil. He lacks a moral spectrum, entirely, preferring to rely on ethics and survival instincts.
Shibin Ei Phandri is dead. He was Moghendhim's older brother, and died in an assassination by their middle brother Kaliei. Moghendhim found him dying, and Shibin's sheer force of will and desire to live allowed him to force his spirit into his youngest brother's body. (And, you know, it might also have had something to do with his oldest sister being less than careful where she dropped her divine items...)
Shibin is always and only there when Moghendhim needs him most. Every time Moghendhim is struck, Shibin Ei makes a contested Ego roll against Moghendhim's Willpower, to take control. While Shibin is consistently aware of Moghendhim, Moghendhim has no awareness at all of Shibin, believing his brother long dead.
Shibin Ei does not exist. At least he isn't real to Moghendhim, but he's real enough to those who cross Moghendhim. Shibin Ei, "the inner blade", is Moghendhim's self-contained guardian assassin. Never mind the angels, here; destroy the problem, so it does not try again at a less appropriate time. A devout worshipper of Iblis, Lord of Retribution, God of Assassins, Shibin Ei is neither indiscriminate nor uncivil. His blades are aimed firmly at those who harm his host, and those who see his blades are unlikely to survive the experience.
Born in the gleam of a dagger, Shibin Ei is all the sides of drow that Moghendhim never mastered. Moghendhim had no application for the training of the Starbright Hall academy, but he absorbed its meaning and nuances, just the same. Not fond of the sight of his own blood, he rarely applied the techniques. Late one night, Moghendhim's oldest brother slipped into his room to rid the Phandri Liyusu of their disgrace permanently. Shibin Ei awoke for the first time to the smell of anticipation surrounding Tamoeiko, and the reflection of his eyes in the dagger, and the dagger in Tamoeiko's eyes. Faster than Moghendhim had ever moved, Shibin Ei twisted the dagger from Tamoeiko's fingers, and breathing a swift prayer to the Lord of Vengeance, slit the young drow's throat, catching the blood in a glass. When the glass was full, Shibin Ei carried the deceased Tamoeiko back to his own room and laid him in bed, eyes closed, hands crossed on his chest. Shibin Ei slept.
Later that week, after Tamoeiko's funeral, the Festival of Winterdark was held beneath Starbright Hall. Moghendhim did not go; he feared that his classmates would call for his sacrifice to the Soul of Winter. Shibin Ei had no such compunctions. After painting his face in the coagulated, terror-tainted blood of Tamoeiko, he dressed in Moghendhim's best clothes, fine silk and leather and fur, as befits a son of the Phandri Liyusu, and set out to the Grand Ball.
It is said that an animal can smell the pheromonal shifts of its own kind, and when the drow at the ball smelled Tamoeiko's fear laid over Shibin Ei's arrogance, they were at least unnerved, and gazed at what they thought was Moghendhim with barely concealed horror, and respect for his skill in avoiding assassination. Only one looked at him disappointedly; Tzusan of Linyon Liyusu. Shibin Ei searched for the reason, and found that she was a friend of Moghendhim's who appreciated his less murderous nature. Shibin Ei, always desiring to protect Moghendhim, quickly went to speak with her, explaining that he (well, Moghendhim) had killed Tamoeiko in self defense, and wore the blood so that no one else would try, because he did not like to kill. Tzusan accepted Shibin Ei's explanation, and called him clever. She apologised for thinking him barbaric, and promised never to speak of the horror again. Shibin Ei gave thanks, and slipped away before he stole what belonged to his host.
One by one, the Phandri Liyusu who were closest to Moghendhim began to disappear, some to resurface dead, some never to resurface. Shibin Ei would not stand for his host being called an abomination and a slaughterer of the family's pride. Soon, little family remained -- one sister and a few aunts -- and Shibin Ei decided it was time to go. Where, he did not know, but not beneath Starbright anymore. During an academy examination, a raid on a surface village, Shibin Ei caused Moghendhim to shoot an upperclassman with a crossbow bolt. Moghendhim lived through the reprimand and the punishment, and after it, the journey to the surface and a time of unconsciousness following the first few punches. Shibin Ei was the reason for the blackout. Pushing through Moghendhim's terror, he quickly killed three drow who were not expecting him to attack. Drinking the blood from the slit throat of the third, he impressed upon the others to go home and speak no more of the night. It was after they left that Shibin Ei discovered the broken body of Tzusan Linyon. He could not let Moghendhim see her, nor could he let her die. Touching her, he found that she still barely breathed, and he ran to search the three corpses in the hopes that some remedy might be found. He was in luck, and managed to find enough herbs to stabilise her, but she was too weak to travel, so he covered her with a cloak and waited some hours at her side, fighting to keep Moghendhim buried. Just before daybreak, she awoke for some moments, thinking that Moghendhim sat beside her. Shibin Ei spoke, "I have saved you from them. I canot stay, but I advise you leave Starbright, and make your life in Midian, or farther. I do not know if they will follow, little rabbit." Tzusan clutched his hand and begged him not to leave, but he explained that it was so they would follow him and leave her be. "Limi'go zin..." she whispered, closing her eyes to sleep again, "Homu'zin shiyon hayoka." Shibin Ei shed his first and last tear, and walked another four miles before resting, and allowing Moghendhim's return.
Shibin Ei rested ten years, and Moghendhim sometimes sees Tzusan's broken face in his dreams.