Aigis (romanized as Aegis in Japanese) is a character from Persona 3. She is an Anti-Shadow Suppression Weapon (seemingly the last one in existence) and a member of S.E.E.S. who also attends Gekkoukan High School. She is a machine that gradually awakens to human emotions.
She is also the main protagonist of The Answer, the epilogue of FES, and its remake as part of the Persona 3 Reload Expansion Pass, Episode Aigis - The Answer.
Aigis' initial personality is simply a robot designed to obey orders, although she is drawn to the protagonist and states that it is very important for her to be by his side, going so far as to hug them in front of everyone. Her desire to protect the protagonist is so strong, in fact, that she was able to overcome Ikutsuki's programming and free the entire team from their shackles, when Ikutsuki had attempted to sacrifice them to bring forth the Fall. As a result of having no emotions, Aigis' social skills are more-or-less non-existent; it's frequently noted on-screen that while she may look human, she is far from passing as such.
She is prone to doing very strange and socially unacceptable things, such as breaking into the protagonist's room to wake him up and requesting to be on standby in their room, which Yukari calls her out for. A video recording shows that she has a habit of breaking into his dorm room at night in order to check on him, even going so far as to keep a record of how long it takes her to pick the lock, In Falling Down, she even goes so far as to sneak into the boys' rooms during the group's stay in Kyoto, claiming it was unfair that she and the protagonist weren't in the same room. Lack of social grace notwithstanding, Aigis is nonetheless very polite to everybody, always using the honorific '-san' when addressing them. In the original Japanese version, she often ends her sentences with "de arimasu" prior to developing emotions.
She is shown to be able to understand Koromaru and often translates for the others, though she is shown to be able to understand dogs in general. She states that dogs don't have a language, but speech is not the only way of communication, with The Answer revealing that she can understand Koromaru's thoughts and feelings. Arena reveals that this is because it was inherited from the 5th Generation Anti-Shadow weapons, one of who took time to communicate with a puppy named Snowy. In Persona 4 Arena Ultimax, Aigis meets him, now an old dog.
In November, when Ryoji Mochizuki first transfers to Gekkoukan High, Aigis immediately becomes suspicious of him and warns the protagonist to be wary of him, saying that he is dangerous, albeit for reasons she can't quite explain. It's around this time that Aigis starts to feel some degree of human emotion; she admits to the rest of the group that she envies them, saying that they know what it means to live, while she isn't "living" so much as "functioning." During the next full moon, she encounters Ryoji and realizes why she was so suspicious of him; he is the Appraiser of Death, who she sealed away ten years ago in the body of a nearby boy; that boy was the protagonist, which is why she wanted to be by his side so much. After being grievously damaged in her battle with Ryoji, Aigis feels immense grief before she ceases functioning, believing herself to be "worthless" as she has been unable to fulfill her purpose as a machine.
Toward the end of December, after being repaired by the Kirijo Group, Aigis' simulated computer software personality (artificial intelligence) develops human emotions, and she becomes compassionate and loyal to her friends, though she struggles to fully understand her new emotions. She deeply regrets imprisoning Ryoji inside the protagonist, believing that they wouldn't be suffering if she hadn't. Initially, Aigis desires for her friends to kill Ryoji, as she can't bear to see her friends suffer and believes they are wasting their lives trying to fight Nyx. She still considers herself as a mere machine whose purpose is to destroy Shadows, and asks what her purpose is if she can't defeat them.
The group replies that she's the only one who can answer that question but as long as they're alive, they have to do something. It is then that Aigis realizes that someone doesn't have to save the world in order to find meaning in life, and that more often than not, it can be simpler, such as taking care of someone or something, even a pet. She decides to live on so that she can protect her friends and fight alongside them and gains a renewed sense of purpose, which triggers the evolution of her Persona.
Aigis' Social Link revolves largely around trying to understand her new emotions; she frequently talks about things that are new to her or that she never gave any thought to before, such as whether or not she likes something or the importance of a shrine. She states that she now understands that living beings are guided by feelings rather than facts, and that was what guided Koromaru to stay at his master's shrine long after his death. She also grows to view her room as unwelcoming, and can't believe she used to think it was normal. After being bitten by a dog, which ends up hurting it instead, Aigis is reminded of an important truth; while her heart may become more human, her body will forever remain mechanical.
In general, the more human she becomes, the more she realizes she will never truly be human herself, resulting in her having an identity crisis. Eventually, however, she realizes what had pained her; as a machine, she cannot die and so she will inevitably outlive the protagonist, who she has fallen in love with, but if that is the case, she can stay by his side until then (which ends up being very soon after). Aigis falls for the protagonist regardless of gender, even expressing lament towards not being a male during the female protagonist Social Link, though she gets over it by the end. In Persona Q, if she's chosen as the destined partner of Yu Narukami, she will refuse, insisting that the protagonist of Persona 3 is her most important person.
After the death of the protagonist, Aigis is so devastated that she once again loses the will to live and wishes to return to being a mere machine, as she had promised to always protect him and be by his side. She apparently found herself unable to face him, as she was the only one who didn't attend his funeral. However, she is still shown to be very kind, as she warms up to Metis quicker than the rest of the group, even giving her permission to call her "Sister."
When the group are having an argument about what to do with the keys, Aigis is completely unsure about what to do, not being able to decide whether the past or the present was more important. After defeating Koromaru and Junpei, Aigis decides that fighting her friends is too much to bear and decides to give up her key to Yukari and Mitsuru, much to Metis' devastation as she doesn't want her to die, and she believes giving up her key will kill her. After a talk with Metis, Aigis learns something; strengthening the bonds of friendship doesn't mean the pain of living will stop, as pain is a natural part of life. She also learns she can still fulfill her promise to the protagonist.
It is then that she decides not to change the past, but to bear the burden of the protagonist's death and continue living towards the future. After defeating Erebus, Aigis fuses back with Metis, and returns to the person she was after the Kirijo Group repaired her, and decides to return to school with her friends. Over The Answer, she ultimately develops into a sweet, gentle, empathetic and strong-hearted girl with a talent for leadership, and regains her will to live. Yukari even admits that out of all of SEES, Aigis cared about the protagonist the most, which is why out of all of them, she was the one who inherited his power.
