- "Could you please listen to this selfish request of mine? Please... don't forget about me."
- —Ennis to Isaac and Miria
Ennis (エニス Enisu) is Szilard's homunculus, although not his first creation. She was created as his subordinate, and is supposed to have no thoughts or emotion when executing his commands. However, after being told to devour an alchemist by Szilard's command, she establishes a sense of right and wrong. After meeting Isaac, Miria and Firo, she gains more human emotions, as well as independent thought. Eventually, she helps Firo by giving him the necessary knowledge to destroy Szilard. A year later she adopts Czeslaw as her younger brother. After seventy years of developing her newfound emotions, she marries Firo Prochainezo around 1986, but they don't have a honeymoon until 2002, forced by Isaac and Miria. For their honeymoon, Firo and Ennis with Czes embark for Japan aboard the cruise ship Entrance.
Ennis was an emotionless, blindly obedient slave to Szilard Quates until the day she killed an immortal under his command. In the the process, she took all of his knowledge and memories and learned of sin and morality for the very first time. Though she was plagued with guilt due to her part in the murder of all sorts of people before and since, Ennis had no other option than to continue to obey or die, and Szilard had ensured from early on that she feared the permanent death that he could deliver at any time. She envied the people who complained that there was no meaning in their existence, because she knew her purpose all too well--she was the tool and weapon of a man she could never hope to escape, and was expected to fulfill her orders without thought or hesitation. Ennis was able to do this for the most part, as Szilard tended to prefer killing people rather than having her do it (mainly so he could have their knowledge for himself), but when it came to killing one of Szilard's underlings for failing to keep the elixir safe, she instead brought him back to her master so that he could explain himself properly. Unfortunately, the man was killed anyway and she was berated for making excuses.
Ennis managed to survive by clinging onto and savoring the moments of silence in-between orders, causing her to become a quiet and withdrawn individual, only talking when necessary, and even then only in formal and clipped speech. Outside of her comfort zone, though (such as when interacting with loud and nonsensical people) Ennis can be very hesitant and shy. In order to protect herself, she had no choice but to hide her new emotional capabilities from Szilard, and so became skilled in tucking her feelings away so she could maintain a neutral expression in his presence and while fulfilling orders--in fact, doing so likely made it much easier for her to accomplish the worst of her tasks, and it was also helpful that she could set aside all personal thoughts in order to fully focus on one thing at a time (such as following a detailed map of Manhattan stored in her memories in order to reach various destinations). However, when she met and made friends with Isaac and Miria for the first time, she became honestly and fiercely loyal to them to the point where she nearly threw her life away to keep them safe. Additionally, remembering what her life was like when she was limited only to the knowledge Szilard would entrust to her, Ennis began to feel sympathetic toward Firo once she understood that he had no idea what was going on or why Szilard was attacking Maiza. She was very willing to fully explain the situation to him--even going so far as to use smaller words upon his request when she got a little too technical.
When Szilard was killed, Ennis, no longer his slave, settled into a more carefree existence and slowly began to express herself, most apparent in her wish to have people she could call family in her life. Due to her unique creation and life experience, Ennis is mentally and physically mature, but slow to grow emotionally. Despite her lack of experience with emotions, though, Ennis is extremely smart and observant, noticing things that easily slip by another's attention. While she tends to keep to herself rather than approaching others on her own, she can be easily pulled into excitable people's shenanigans with minimal effort, and is quick to discover that she's also having fun alongside them.
Ennis was Szilard Quates' last homunculus, created after the previous ones eventually turned on him. However, as he used his own immortal cells to create them, killing them was as simple as willing them to die. Szilard was unaware of it, but Ennis, whose knowledge of emotion was previously limited only to the fear of death at his hands, had begun to become capable of much more after she'd been ordered to kill an immortal and received knowledge of morality and much more for the first time as a result. She feels immensely guilty about her part in the murders of the past and present, but has no other choices other than obedience and death.
Taking a break, the two of them returned to New York City in 1930 when they learned that Szilard's subordinates had completed the Cure-All Elixir, but due to a certain string of events, the storehouse burned to the ground and the bottles saved from the fire were stolen. Ennis was sent out to recover the elixir from the thieves, but as it continued to change hands, she experienced a few fateful encounters, first by meeting an immediately lovestruck young man named Firo Prochainezo about to be promoted within his Camorra, the Martillo Family, and then by running into a pair of thieves, Isaac Dian and Miria Harvent, who became her very first friends after she saved them from a group of violent street thugs. As the day went on, the elixir ended up being served at Firo's promotion party, creating a whole new generation of immortals, and Maiza was discovered within that same organization. When Szilard appeared to kill him, the entire Camorra was pulled into the struggle along with Isaac and Miria. When the two thieves were put in danger, Ennis betrayed Szilard in order to give them an opportunity to escape, but was easily paralyzed by her master with a single thought. Isaac and Miria, wanting to save her, managed to stall Szilard until Firo and the rest of the Camorra reappeared. In the battle that ensued, Firo followed Ennis's instructions and managed to kill Szilard, acquiring all his knowledge and memories in the process. Because of that, he was able to save her.
Ennis began to live with Firo soon after, grateful to him for saving her life and wanting to thank him by helping him however she could, but due to her slow emotional growth, she did not have much ability to return his affection for quite some time, and, in fact, was not even aware of his feelings for many years. Meanwhile, in 1931, after misinterpreting a letter Ennis sent them, Isaac and Miria assumed that she wanted a little brother, even though what she actually mentioned was her regret at never being able to meet her long deceased homunculus brothers. The two of them ended up bringing her Czeslaw Meyer, a young boy who became immortal in 1711, as a 'souvenir' when they returned to New York, and he began to live with her and Firo after she adopted him as her younger brother. Along with him, Firo, Isaac, Miria, the Martillo Family and their allies, Ennis was finally able to have something resembling a family to call her own.
Ennis possesses absolute immortality, unable to die, age, get sick, or be permanently wounded. However, even though she is a homunculus, Ennis is also subject to the 'rules' of immortal humans; she cannot use pseudonyms among other immortals, is able to transfer knowledge to other immortals by placing her left hand upon their head and thinking about the information she wishes to share, and 'devouring' other immortals through her right hand by touching their head and wishing to 'eat' them, effectively ending the other immortal's life and granting her all of the deceased immortal's knowledge.
Ennis possess extremely sharp senses and quick reflexes as shown when she could easily dodge multiple attacks from multiple armed attackers. She is capable of fighting and taking down multiple armed-thugs while while unarmed with little trouble. She has extensive knowledge all given to her by Szilard in order for her to carry out her duties.
Isaac and Miria - After getting off to a rough start when she almost runs them over, she meets them personally after saving the pair from Dallas Genoard and his gang. They thank her enthusiastically, becoming her first friends. The three rejoin on much worse terms outside the Alveare, when Isaac and Miria steal Szilard's car and run over him, Dallas, and his gang. After recovering, Szilard orders Ennis to subdue the couple while he attempts to devour Maiza. Knowing that he will kill her as soon as she shows resistance but refusing to betray her only friends, Ennis asks Isaac and Miria to remember her before she turns to sabotage Szilard. Firo eventually kills him, and Isaac and Miria are saved. Ennis is shown to be close friends with them as they helped her overcome her fear of dying to her creator.
Szilard Quates - Her creator and former master.
Firo Prochainezo - Both met outside Barnes' burning house, bumping into each other. In the novels, Firo became instantly infatuated with her, while the anime has him trying to give her back an unimportant clothing accesory. After 50 years, Firo and Ennis get married.
Czeslaw Meyer - Czes is Ennis' adopted 'younger' brother. He was given to her by Isaac and Miria as a gift after a misunderstanding on a letter sent to them about her past 'brothers', Szilard's other homunculi before her, instead believing she was just lonely. It's mentioned that Czes and Ennis frequently spend time together, so it's safe to assume that they have a close relationship. The fact that Czes is nearly 200 years older than her does not seem to trouble her as he rarely acts his age around her in to avoid being awkward, making their role as siblings more enjoyable.