Sunni Moon is a "free agent"--an assassin, mercenary, Stephen April's personal "hit-woman" and one of his several lovers.  She is also, simply put, crazy--a psychotic, murdering maniac who takes care of the "dirty deeds" for April, acting as his "long arm" in dealings with others.  In 2385 Sunni's twin sister, Kitti, a spy for the Alliance, infiltrated the I.S.S. Arcadia and passed herself off as Sunni in an attempt to assassinate April, but failed and was killed by Tabatha Brisk... for which Moon has yet to get even.  Despite her lunacy, Moon is generally loyal to April and the Empire.