Personality: 

Emotionless, steady, and objective focused. Es is the perfect soldier, her mission always comes first. When she first met Tōya Kagari, she did not care for him or any other person, being willing to hurt and even kill others that she was 'friends' with just so she could complete a mission. If Es did not understand a term, mainly because of the informality or colloquial speech, then she would forwardly ask what said term means, leading to unique, and awkward situations. For a time, she possessed no opinions due to her little interaction with people outside of the Agency, as well as this, Es possessed a habit of taking things too literally, annoying Tōya as he put up with her awkward social tendencies.

Possibly because of her initial lack of understanding towards humans, Es was prone to revealing information to others unnecessarily, and would often act in a robotic manner towards anyone conversing with her. She would also ignore the orders of anyone who was not her superior or essential to her mission objectives, leading to humorous circumstances; it was because of this tendency that she was seen as unerringly stubborn.

Her time with Tōya softened her, and she was able to feel more emotions as time progressed. When she failed to protect him from being knocked out by Kazuto Kotetsu, she gave him a heartfelt apology; even when Akira Kamewari went missing, Es became a sort of emotional crutch for Tōya to lean on. When she fell out with Tōya, she became visibly upset, signalling another emotional growth for her, albeit's discovery being bittersweet. Furthermore, she began to disobey direct orders from her ward, even beginning to emit emotion into her speech; the most notable example being when she outright denied detaining Tōya, instead opting to protect him from the Agency unit sent to retrieve him. When she inherited the Embryo, Es expressed a profound sadness at making Tōya bare the same burden as her since she felt herself as irredeemable after having taken so many lives.

She has also learned the true meaning of being family thanks to her interactions with Hinata and Yuki, which allowed her true self, a kind and noble girl, to emerge. She also developed a strong romantic love toward Tōya, who she labels as her dearest one and the most important person in her life. However, due to seeing her true love and her friends being killed by Freaks sent her into despair at being unable to save them and scattered her memories to escape from her heartbreak, showing how much they mean to her.

However, upon her rebirth in Lost: Memories, when she lost her memories, she became notably more cheerful and smiled more often, but still retains her curious outlook on life. Upon recovering her memories, she regained her proper and formal tone of speaking, along with retaining her newfound cheerfulness. After saving Tōya and the others, as well as recalling her (Nobody's) friend "Me", she has vowed to keep moving forward, no longer chained by her lonely past with newfound faith in herself, her friends, and the boy she loves, finally obtaining happiness in her life and no longer giving into despair.