This Article Contains Spoilers - WARNING: This article contains major spoilers. If you do not wish to know vital information on plot / character elements in a story, you may not wish to read beyond this warning: We hold no responsibility for any negative effects these facts may have on your enjoyment of said media should you continue. That is all.
Izanami is the true main antagonist and final boss from Persona 4.
Izanami plays an important role in Persona 4 (it can be argued that she is the game's true antagonist). Intrigued by humanities' true desire, Izanami takes the form of a human, and bestowed various people their latent powers of invoking Personas. Izanami believed, that by observing the ones who have awakened would carry out humanities' true desire.
Disguising as an Attendant working in the Moel Gas Station of Yasoinaba, Izanami awakened Tohru Adachi, Taro Namatame, and finally, the Protagonist' potential of invoking Personas. It is unknown exactly how many humans Izanami awakened, however, she implies that many have been awakened by her.
Using her identity as an attendant of the gas station, Izanami spread rumors regarding the urban legend of the Midnight Channel. As the Midnight Channel reflects the images of the viewers' desires, Izanami believed that this would make her understand better about humanity's wishes. However, Adachi, one of the awakened ones, uses his powers for murder, and carries out the belief of humanities' insecurities, leading Izanami to believe that what humanity actually wishes is a world of oblivion and stillness, and thus she subjects to overrun the world with Shadows. Acknowledging Adachi's plans, Izanami created the god of fog, Ameno-sagiri, and later, the Midnight Channel.
Izanami begins to set her plans in motion; upon the Protagonist' first meeting with Izanami, taking the identity of the Moel Gas Station Attendant, Izanami takes an interest within the Protagonist's potential, and decides to give his latent talent of invoking a Persona a little push via a handshake. In actuality, Izanami plans to use the Protagonist as a catalyst to awaken the potential of invoking Persona of those close to him, so they could carry out her plans.
After the Protagonist' first interaction with the Gas Attendant, Izanami visits the Protagonist in his dream. In there, Izanami taunts the Protagonist's wish to reach the truth, but asks him to follow her if he truly wishes to seek the truth. Izanami's plans of using the Protagonist eventually was a success. In the events of Normal Ending however, the Protagonist's Wild Card ability and his determination is something she did not foresee. Ignoring the urges of killing Taro Namatame, the wrong suspect of the murders, allows the Investigation Team to eventually find out the true culprit: Tohru Adachi.
In the events of the True Ending, after defeating Tohru Adachi and defying Ameno-sagiri's plans to overrun the world with Shadows, the Protagonist manages to find out the Attendant's true identity as Izanami, and upon realizing the Protagonist's determination of seeking the truth and stopping her from carrying out her plans again, Izanami chastises the Protagonist's persistence to seek the truth, and tells him that she shall await the Protagonist's defeat in the "other world". Izanami's reality within the Midnight Channel, Yomotsu Hirasaka, derives from a place taken from the Japanese mythology of Izanagi and Izanami. It also takes on the appearance of traditional Japanese Shinto Shrines.
In the Protagonist's final confrontation with Izanami, she faces the party with her goddess form, but it was eventually revealed to be a fabricated appearance when the Protagonist uses the Orb of Sight, an item given by Igor to shine upon the truth. Having her facade taken away, Izanami reveals her true form as Izanami-no-Okami, a rotting, death-ridden being. Izanami-no-Okami later sends the Protagonist's comrades to the underworld, and finally, the Protagonist himself. As the Protagonist is about to give up, he hears the voices of his friends, encouraging him.
Accumulating the bonds and powers of the Social Links he had forged thus far, the Protagonist channels the powers to his initial Persona, Izanagi, transmogrifying Izanagi to his true form, Izanagi-no-Okami. Bemused by the Protagonist's powers, Izanami-no-Okami repeatedly attacks the Protagonist, but is surprised to see the Protagonist enduring all her attacks. Angrily asking how the will of so few could defy a divine will, the Protagonist ultimately summons Izanagi-no-Okami, ending Izanami with one powerful attack, known as "Myriad Truths"
Upon Izanami's defeat, Izanami exclaims that she will not interfere with humanity anymore. She encourages them to live and face their own decisions, but cannot guarantee their happiness, and fades away.
Despite Izanami's antagonistic nature, she truly wishes for humanity's happiness, as evident that she later congratulates the Investigation Team for discovering the truth, as well as defeating her.