Izayoi

was the human mother of Inuyasha, whom the Inu no Taishō fell in love with.

Manga
Rumiko Takahashi states in Zusetsutaizan Ōgikaiden that Izayoi (or simply "Inuyasha's mother" as she has no official name in the original series) was the daughter of a wealthy lord, though the family had fallen into hard times. She also states that Inuyasha was born in an isolated location and into poverty. She is always portrayed in fine clothing, however, with a solemn yet graceful appearance. Little is known about her life, including how she met the demon lord who would become Inuyasha's father, although it appears that the two shared a close bond - the sword, Tessaiga, was created to protect her, as was the Robe of the Fire Rat. In a rather unexpected turn of events, Sesshōmaru's mother makes an appearance late in the series, bringing about even more unanswered questions. She remarks, however, how her son Sesshōmaru is similar to his father in regard to his care of the human child Rin.

The character of Inuyasha's mother only appears once as herself in the series, and has no lines. The character is introduced by Sesshōmaru, Inuyasha's elder half-brother, who uses a yōkai to make a perfect duplicate of Izayoi in order to trick Inuyasha into revealing the whereabouts of their father's demon sword, the Tessaiga. Sesshōmaru blames Izayoi for his father's death, claiming that she had made the Inu no Taishō weak which lead to his death. The manga never elaborates on Sesshōmaru's claim, however the third InuYasha movie attempts to fill the gap. The ruse is eventually discovered, however, although not before the location of the sword is found.

Throughout the rest of the rest of the series, Inuyasha's mother makes no other appearances and Inuyasha himself does not reference her.

Anime
Once again, her character remains known only as "Inuyasha's mother" and her introduction and character remains the same as in the manga series. The anime, however, adds a few extra scenes, showing a young Inuyasha in a lavish garden at a wealthy estate. He attempts to join the other nobles in a game of temari ball, but they toss the ball away and leave as he goes to retrieve it. Inuyasha later recalls this was the first time he saw his mother's tears. Inuyasha was left two things from his mother, his Robe of the Fire-Rat and her lip-coloring makeup. Inuyasha later gave the makeup to Kikyō.

When Kagome came down with a cold, it was revealed that Izayoi taught Inuyasha how to make a medicinal brew. It contains several kinds of herbal leaves and roots, along with at least three different kinds of liver. Sota kept him from revealing to Kagome that he had used raw liver instead of dried ones like his mother did.

InuYasha the Movie: Swords of an Honorable Ruler
The third InuYasha movie provides us with details about Inuyasha's birth and how the Inu no Taishō died. Izayoi is the daughter of a wealthy feudal lord about to give birth to a child, an event that causes the samurai Takemaru no Setsuna, Izayoi's former suitor, to hold her captive in order to lure the child's father, the Inu no Taishō, into a trap so he can kill the Daiyōkai. Though Izayoi told Takemaru to leave in order to spare him from the Inu Daiyōkai's wrath, Takemaru admits that he still has feelings of love for her, but that he will not allow her to give birth to a half-demon. He attempts to kill both Izayoi and the unborn child, but leaves before noticing she is able to give birth alive to Inuyasha before eventually dying.

The Inu no Taishō easily overpowered Takemaru's men and rushes to Izayoi's aide, only to discover his beloved dead. Fortunately, he is able to use Tenseiga to revive her. The Inu no Taishō gives Izayoi the Robe of the Fire Rat and then orders her to escape with their son, whom he names "Inuyasha". She follows her beloved's instructions and leaves. Unfortunately, her lover was already injured badly in an earlier battle with the dragon yōkai, Ryūkotsusei. The injuries weakened the Inu no Taishō enough so that when the mansion collapses on both him and Takemaru, he dies along with Takemaru. This sets up Izayoi to raise Inuyasha on her own.

It is also shown in the series that Inuyasha still tends to his mother's grave, despite it being over 150 years since her death.

Personality
Izayoi was shown to be a kind and gentle woman who cared much for Inuyasha and the Inu no Taishō. Although little is shown about her both in the anime and manga, in the third InuYasha movie, it is shown how the Inu no Taishō loves her and so does she. She is kind with Takemaru, the man who admitted he loved her. Izayoi wanted to save Takemaru from the Inu no Taishō's wrath, but in the end they both died in the fire.

Later on in the anime, Inuyasha has a flashback in which her mother comforts him when some people call young Inuyasha a "half-breed". She, however, was sad at that point, for she could only imagine what life could be like for her son: not fitting into either the human or demon world. How she died is unknown, but Inuyasha must really love his mother, for he takes fresh flowers to her grave every once in a while, likewise the only comment Inuyasha makes about her passing is that 'it wasn't her fault'. She died while Inuyasha was still a child, as another flashback shows a young Inuyasha, perhaps 7-10 years old, out on his own in the woods, running for his life from Oni.

Relationships
Unfortunately, very little is known about the relationship that Izayoi and the Inu no Taishō had. In Zusetsutaizan Ōgikaiden book, she is, however, listed as his "wife". The circumstances that led to their meeting are unknown. However, both appear romantically affectionate towards one another. Izayoi refers to him as and the Inu no Taishō clearly has only her in mind after his battle with Ryūkotsusei: instead of tending to his wounds, he rushes to her side, only to find her dead and cradling their child (thankfully, he is able to use Tenseiga to revive her). Before he died, he told her "Izayoi, you must survive and live a long life, live long and well with Inuyasha." It clearly shows he loved her.
 * Inu no Taishō

The half demon son of Izayoi and the Inu no Taishō and younger half-brother of Sesshōmaru. Inuyasha had a special relationship with his mother, who raised her son alone until her death, and becomes very defensive when she is brought up. He prefers not to talk about her, which shows he misses her a lot. According to the third movie, Inuyasha will occasionally visit his mother's grave to place new flowers. She loved and cared for her son wholeheartedly, and realized he would have a difficult life being a half-demon.
 * Inuyasha

It is unknown if Izayoi cared for Sesshōmaru or not, but it is shown that Sesshōmaru despised her immensely because she was human and he believed their relationship hastened his father's death.
 * Sesshōmaru

Trivia

 * The character of Inuyasha's mother is not officially given a name in the manga or anime series and was variously known as simply "Inuyasha's mother" or "Inumama". She is given the name Izayoi in the third movie and, although it may not be considered canon to the manga series or even the anime series, most fans will use the name Izayoi for simplicity.
 * Izayoi is the name given to the night of the 16th of every month. The Japanese believe that on that date, the night is more beautiful.
 * Rumiko Takahashi, the series creator, has a tendency to draw noble women in a very similar manner. Izayoi's design is not much different from other characters of high rank, apart from the color and design on her kimono.
 * Izayoi is only ever depicted wearing a Jūni-hitoe, an extremely elegant and highly complex kimono, that was only worn by high-ranking court-ladies in Japan. Literally translated, "Jūni-hitoe" means a "twelve-layer robe".
 * Due to her birthright as a hime, this by extension makes her son, Inuyasha, of noble blood on both the human and demon sides of his family as his father is the demon lord of the West.