Xi Wangmu (西王母), who means "Queen Mother of the West", or Seioubo in Japan, is an ancient Chinese goddess, also known in Japan and Korea. She had a human form with a leopard's tail, tiger's teeth and wore a jade tiara. She had three azure birds in her charge that tended to her needs by bringing her food and nourishment. In early Chinese mythology, she was the goddess of diseases, calamities and slaughter. She would later gain immortality and enlightenment through cultivating the Dao and became one of the highest deities worshiped in the Taoist pantheon. She took her throne on Mount Kunlun and became the goddess of immortality guarding the Taozi (Peaches of Immortality).
Numerous rulers throughout China have legends and folklore attributed to them on how they went to her hoping to learn the secrets of immortality only to fail in the end. The most famous of which is King Mu of the Zhou Dynasty, whom she took in as a pupil and lover for a short period of time, but like all the others King Mu was unable to gain immortality. She would reach the height of her popularity during the Tang Dynasty where numerous cults centered around her sprung up and she became the subject of many literary works.
"An ancient Chinese goddess who ruled over the Kunlun mountains. She was worshipped during the Han Dynasty. She looks like a human, but is said to have the teeth of a tiger and tail of a leopard. She kept the peaches of immortality, which Wu Kong stole and ate."
—Shin Megami Tensei: Strange Journey compendium
Shin Megami Tensei IV
A foreign demon who is the self-proclaimed Empress of Ikebukuro who had placed a barrier around it, as well as setting up her own Domain. She devours the humans of the city even though she finds their taste lacking, and leads a large group of foreign demons. Her body is near invulnerable to all attacks, each only dealing one damage point to her regardless of stats, even if the attack hits her weakness.
She finds the Ring of Gaea members to be simple-minded when they attack her, and devoured them all, though she enjoys how feisty Kaga is when compared to others. However, by devouring them she unwittingly leads to her defeat - the Gaea members are too much for her and attack her from the inside, weakening her enough for her defense to fall, allowing for damage to start piling up and ultimately kill her.
Xi Wangmu apparently also attempted to attack Ikebukuro in Infernal Tokyo's timeline. However, she was never able to establish a strong hold on it as she was slain fairly quickly by King Kenji.
Shin Megami Tensei IV Apocalypse
Xi Wangmu can teach Nanashi the Makarakarn, Myriad Arrows, Lullaby and Doping skills through her Demon Whisper. She benefits from learning support, Gun and ailment skills.
Known as Seioubo, she is a Persona of the Empress Arcana. In order to fuse her, the protagonist must have the Emperor Wu's Peach Totem which can be acquired as a prize in the Casino. Upon being returned to the Velvet Room at MAX Rank, Seioubo produces a Caesar Helm, the most powerful headgear in the game.
Devil Survivor 2 Record Breaker
"A goddess revered in ancient China who grew popular during the Han dynasty. Her palace is said to be atop the mythological Mt. Kunlun. She is mostly human in appearance, with a distinctive headdress as well as the tail of a panther and the teeth of a tiger. Originally she was said to govern the Five Calamities, but later came to be depicted as a beautiful sage and enshrined as the ruler of Mt. Kunlun. Among her legendary encounters was Sun Wukong, who stole and ate the Peaches of Immortality."
—Devil Survivor 2 Record Breaker compendium
Xi Wangmu is only available after finishing the Triangulum Arc at least once. She can only be fused using Da Peng and Bai Ze.