Age 4: Death of subject's parents, induction of subject into Imperial care.
Age 6: Cleansing of subject's past memories upon Correction Throne, subsequent induction of subject into Schola Progenium. Lack of prior inclinations leads to substantial compliance, though somewhat sadistic tendencies present themselves frequently.
Age 15: Murder of a Drill Abbot by subject after excessive punishment and abuse, consequent set-up of hated fellow student as perpetrator. Student executed, blame believed to be successfully shifted by subject.
Age 17: Subject attacked by another student with a boltgun; attacker ordered to do so as part of their Trials of Compliance in order to show suitable Commissarial traits. Heated battle and severe injury ensues; attacker is eventually gutted and tortured to death by subject with a pair of eating utensils.
Age 18: Subject's graduation from Schola Progenium. During graduation, member of the Officio Assassinorum reveals to subject that they are fully aware of prior killings, and wish to cultivate the tendency further. Consequent on-ship trial ensues - limited oxygen allows only a minute number of Initiates to reach Holy Terra. Upon arrival, subject and one other student still survive.
Ages 18-28: Training and surgery of subject under Callidus Temple. First inclinations of fighting back against Lord Assassin in charge are met with a gun barrel to the side of the head, and the promise that any hint of future rebellion will be met with instant death. No further issues present themselves, and graduation is reached with little relative notice. Further training of subject continues until induction into Inquisitor Karthis' retinue.
Age 32: First official target given to subject, the leader of a growing Chaos warband. Over next standard Solar year, subject kills and impersonates high-ranking official in leader's retinue, persuading leader to gather recruits from largely-Loyalist worlds in effort to minimise warband's growth, then directing them via their pride to attack heavily defended Forge World to break the warband. Before the leader can reach the battlefield, subject slays him and majority of his retinue with Phase Sword, leaving warband disorganised and easily crushed. Remainder of retinue is killed or captured by Imperial forces.
Age 36: Second official target given to subject, high-ranking Eldar Farseer. Early on in assignment, subject is nearly slain by Eldar strike force as a result of sorcerous foresight; death is faked, and subject consequently kills and impersonates a member of the strike force, making way to Craftworld Saim-Hann. Due to the Farseer's powerful psychic abilities, several weeks are spent moving around the craftworld before subject manages to catch and kill target Farseer and two other high-ranking Eldar with Neural Shredder, escaping Craftworld in pre-prepared Eldar ship. Supposedly, Farseer intended to ambush subject with allies before being killed; subject's inclinations suggest the other Eldar were deliberately manipulated to be killed alongside Farseer.
Ages 37-43: Subject inducted into Inquisitor Karthis' retinue, primarily seeing use in secure data retrieval and general assassination of enemies, only occasionally taking on intended role as infiltrator. Subject is returned to Callidus Temple for scheduled mindscrubbing only infrequently during this time, and never during latter three and a half years of tenure; reason believed to be cultivation of heretical tendencies.
Age 43: Subject declared Excommunicate Traitoris, along with Inquisitor Karthis and other retinue members. Subject's final attempt to communicate with Callidus Temple indicates attachment to fellow retinue members and a desire to see them free of suspicion despite clear evidence otherwise. Whilst indoctrination theoretically precludes corruption, and mindwiping could cleanse heretic thoughts, no risks can be taken with an Assassin.

+++ THOUGHT FOR THE DAY: Delusion is as sure a path to heresy as self-interest. +++

Essidi's personality is somewhat malformed, both for repetitive cleansing of memories and the nature of her role as a Callidus Assassin. She is able to take on the traits of others with incredible ease, and can accurately emulate a target's persona after mere hours, even minutes of observation; she also has an interestingly Eversor-esque tendency to, on making the fatal blow, take out not only the intended target, but also as many people as possible who might take the target's place in the hierarchy, apparently out of a desire to ensure her job is truly completed.
A recent lack of mental formatting has resulted in the development of certain "real" personality traits, specifically tendencies toward sarcasm or over-explanation when asked about certain topics, and growing awareness of the effect her figure has on certain individuals, though she generally bears substantial social skill nonetheless. Her devotion to the Emperor is total, thus her desire being more to absolve her allies of guilt than herself; consequently, her tolerance for heresy and corruption is nil, though her ability to blend in and extreme patience may suggest otherwise to the untrained eye.