Jaesa Willsaam, a Human female Jedi Padawan, was once under the instruction of Jedi Master Nomen Karr. Later, she became the apprentice to the Empire's Wrath, who swayed her away from the Jedi Order to embrace the Sith during the period known as the Cold War.
Born on Alderaan to Gregor and Parvin Willsaam, Jaesa Willsaam spent her formative years as a handmaiden serving Gesselle Organa of House Organa. Her family, lacking in riches, anticipated an improvement in their circumstances through her arranged marriage to an Organa noble. However, destiny intervened when her inherent Force-sensitivity emerged. Recognizing the immense potential for their daughter, her parents permitted her to be taken for training by the Jedi.

Willsaam underwent training in the Force under Jedi Master Yonlach on Tatooine for an unspecified duration. During one of her trials, she confronted a sand demon without weapons and emerged unharmed.
Subsequently, Nomen Karr discerned that Willsaam possessed a rare Force-related ability: the power to perceive and effortlessly discern the authentic nature of other beings. Karr recognized an opportunity to dismantle the intelligence network of his longtime Sith adversary, Darth Baras, through her. At her master's direction, Willsaam identified several of Baras' operatives located on Balmorra and Nar Shaddaa.
Baras discovered her existence and unique talent—though not her specific identity—on Dromund Kaas by extracting information through the torture of a captured agent of the Republic. Baras promptly tasked his most promising new apprentice with the mission to seek out and destroy individuals connected to Willsaam's past, hoping to force her out of hiding.
After two of the spies she had exposed were eliminated by the Sith apprentice, Willsaam increasingly sensed the presence of the dark side of the Force. The Sith swiftly began to target individuals close to her. The apprentice initially sought out Master Yonlach on Tatooine. Willsaam's former master, using their Force bond, warned her that the Sith were attempting to lure her out before suffering a painful demise. When Willsaam finally felt the deaths of her parents on Alderaan, she decided to take action. She reached out to the Empire's Wrath to arrange a private meeting without her Master's awareness.
Master Karr quickly learned of Willsaam's scheme and, deeming it unwise and forbidding her from proceeding, dispatched Jedi Knights Zylixx and Ulldin to neutralize the Sith threat. However, the two Knights were easily defeated by the Sith. Karr, determined to eliminate the threat to Willsaam's life, arranged a duel to the death with Darth Baras on Nal Hutta to settle their conflict.
To protect himself and destabilize Karr, Baras sent his powerful apprentice to the duel in his place. As the Jedi Master and Sith apprentice clashed, the Sith manipulated the old Jedi into succumbing to the dark side to further torment Willsaam.

Upon her Jedi Master's defeat, Willsaam emerged from hiding, sensing his torture and witnessing his corrupted state. Initially, she accused the Warrior of corrupting her Master but then entertained the possibility that Karr had concealed this all along. The Warrior urged her to use her power on Karr to uncover the truth. Willsaam complied, but despite detecting dark traits within Karr, she refused to accept it. The Warrior continued to provoke her into unleashing her anger and engaged the Padawan in battle, easily defeating the young Jedi. Defeated, Willsaam became convinced that Karr's teachings about the light side of the Force being stronger than the dark side were false. Karr reminded her that she had not completed her training and promised that when she fully embraced the light side, no Sith could match her.
Nevertheless, Jaesa acknowledged the Warrior's power and agreed to become the Sith's apprentice. Her first act was to kill her former master with her own hands. Despite Karr's pleas for her not to let the Sith turn her into a murderer, Willsaam coldly retorted that the Jedi hypocritically do the same to justify their actions, and decapitated Karr.
Willsaam became a newly appointed Sith apprentice, joining the Sith Warrior as they departed from Nal Hutta. The Warrior was promoted to the rank of Sith Lord for successfully hunting her down, and she became a willing agent of the Empire.
Their adventures spanned the galaxy, as they aimed to undermine both the Republic and the Jedi, working tirelessly to re-ignite open warfare between the Republic and the Sith Empire. She showed devotion to her Master, promising never to follow the Sith traditions involving killing the Master. When her Master was chosen as the Emperor's Wrath, Jaesa was excited, knowing that this would bring them closer to the Sith Emperor and ultimate power, believing that the Wrath could lead the Empire to glory. Ultimately, Jaesa pledged to remain by her Master's side to help mold future apprentices.

Eventually, Jaesa realized that many Sith were leaning towards the light side. With her master's permission, Jaesa spent her free time seeking out Sith who adhered to some aspects of the light side. She eventually learned of Lord Cendence, who was tasked by the Dark Council with eliminating light-side Sith. However, Jaesa grew concerned over Cendence's high kill count. Upon gaining an audience, she quickly discovered that Cendence simply killed whomever he wanted; very few of his targets were light-side Sith. Cendence recognized that Jaesa's power would validate his work. He tried to persuade her to betray her Master, but she simply laughed in his face and killed him. Caliqu, the Dark Council's emissary and Cendence's superior, was present and granted Jaesa Cendence's mandate.
Willsaam continued to serve her master for several years, becoming one of the Wrath's closest friends and confidantes. She stood by their side during the Conquest of Makeb and the Revanite crisis, when the former dark lord Revan attempted to revive the slumbering Sith Emperor, whose previous host body had been killed by the Hero of Tython three years earlier. The victory of the Yavin Coalition brought a brief period of stability to the Sith Empire, which had been on the verge of collapse. To ensure the Sith remained united, Darth Marr made Jaesa's master the "Empire's Wrath," who became Marr's right hand along with Darth Nox, another member of the Dark Council. During her remaining time as the Wrath's apprentice, Willsaam continued to serve both the Sith Lord and the Empire faithfully.

In 3636 BBY, a mysterious army launched an incursion into both Republic and Imperial territory. As Darth Marr organized a joint expedition into Wild Space, the de-facto Emperor's fleet was attacked by another armada of mysterious origin. This battle marked the rise of a third galactic power: the Eternal Empire. Immediately afterward, the Wrath disappeared mysteriously.
Following the Wrath's sudden disappearance from the galactic stage, the Sith Lord's crew began to grieve the loss of their leader. Willsaam seemed less affected by the loss than the others, even becoming slightly annoyed by her friends' constant sorrow. The former apprentice believed that the loss of her master presented the perfect opportunity to expand her own power base, attempting to succeed her master in maintaining the Wrath's influence. She ultimately gained a rival, who attempted to seize the dark center that she had worked so hard to secure.
As a handmaiden and Jedi student, Jaesa was somewhat innocent, inadvertently allowing her mistress to take advantage of her talents. After the murder of her master and parents by Baras's apprentice, Jaesa became unhinged and attempted to challenge the apprentice. Her biggest weaknesses were her recklessness and her reliance on someone strong and dependable. When the apprentice revealed her master's hypocrisy and defeated her in combat, she was easily persuaded to defect and join the Sith. After her defection, she embraced her inner power and willingly served the future Empire's Wrath, unleashing her inner strength through acts of relatively minor sadism in service to the dark side. As she indulged in her passions, she gave little thought to murder or casual relationships, to the point of either engaging in carnal relations with or killing a random Imperial soldier while at a party and being only mildly confused, rather than deeply disturbed, by the acts of passion and potential death, viewing it as "playing hard" since she worked hard.
Jaesa was skilled in wielding a double-bladed lightsaber and demonstrated her proficiency in the Soresu form while fighting the future Emperor's Wrath.
Jaesa also possessed a unique talent similar to Force sight that enabled her to perceive the alignment and personality traits of others. With training, she could scan entire planets and even quadrants of the galaxy, eventually locating Light Sith. However, finding individuals over such distances required focus and time to distinguish identities and locations.
She also had the power to use Force lightning, and was quite skilled in telekinesis. Due to her powers, Jaesa was also adept at both interrogation and diplomacy.

Rachael Leigh Cook provides the voice for Jaesa Willsaam. Jaesa's alignment, whether she remains on the light side or falls to the dark side, is determined by how the Sith Warrior known as the Empire's Wrath recruits her. In an alternative light-side path, her initial action involved eliminating her former master, watching as her new master struck him down, and accepting her fate.
In the original Sith Warrior class storyline, male player characters can pursue a romance with her and eventually marry her, but only if both the player and Jaesa are aligned with the dark side of the Force. However, if the player is also courting Vette, Jaesa expresses jealousy and suggests he ends his relationship with the Twi'lek. If the relationship between the master and apprentice progresses and the player is still romanced with Vette, Jaesa will plead with him to end his relationship with the Twi'lek. Similarly, Vette will also question this, leading to a confrontation between the three characters, and the player must choose between them. If the player desires both, Vette refuses to participate and ends their romance. If both Jaesa and the male Sith Warrior follow the light side and he does not romance Vette, the player has the option of having children with her, as their offspring would possess great advantages. However, the player can have Jaesa's children and still romance with Vette during the romance conversation with Vette later at the end.
If the Alliance Commander is a Sith Warrior, their reunion with Jaesa Willsaam after the Nathema Conspiracy depends on Jaesa's alignment, but not on the player character's gender. Both female and male Sith Warriors can initiate a new romance with her, or the latter can continue a previous romance. If Jaesa has fallen to the dark side, she will begin attacking Alliance troops and personnel on Iokath, leading Lana Beniko to arrest her and bring her to the Commander. Jaesa will tell her master all about how she felt after their disappearance, saying that she tried to get over their presumed death, and will additionally state that they abandoned her and now she wanted revenge. She will state that she deserves to be punished for what she has done and tell her master to go ahead. The player can choose to fight her and kill her, imprison her, or forgive and optionally romance her.

If Jaesa was allowed to remain on the light side, the Alliance Commander will encounter her on Ossus. She will tell them about how she tried to find other light-leaning Sith but could not, and barely escaped from a trap from an enemy posing as a light Sith. She will also explain that she met Master Gnost Dural, who took her to Ossus to redeem her and have her rejoin the Jedi Order, but now that she is reunited with her master, her path is with them. She will ask them to spare Gnost Dural. The Commander will then take her to Odessen, where she will join the Alliance, then she confesses that she has the type of feelings for her master that the Jedi normally forbid and that she considers herself a fool. The player can then choose either to romance her, or simply be a good friend.