Izayoi

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

Manga
Rumiko Takahashi stated in Zusetsutaizan Ōgikaiden that Izayoi (or simply "Inuyasha's mother" as she had no official name in the original series) was the daughter of a wealthy lord, though the family had fallen into hard times. She also stated that Inuyasha was born in an isolated location and into poverty. Little was known about her life, including how she met the demon lord who would become Inuyasha's father, although it appeared that the two shared a close bond - the sword, Tessaiga, that was formed from Inu no Taisho's fang, was created to protect her, as was the Robe of the Fire Rat. In a rather unexpected turn of events, Sesshōmaru's mother made an appearance late in the series, and brought about even more unanswered questions. She remarked, however, how her son Sesshōmaru was similar to his father in regard to his care of the human child he looks after, Rin.

The character of Inuyasha's mother only appeared once as herself in the series, and had no lines. The character was introduced by Sesshōmaru, Inuyasha's elder half-brother, who used 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 blamed Izayoi for his father's death, and claimed that she had made the Inu no Taishō weak which lead to his death. The manga never elaborated on Sesshōmaru's claim. However, the third InuYasha movie attempted to fill the gap. The ruse was eventually discovered, however, although not before the location of the sword was found.

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

Anime
Once again, her character remained known only as "Inuyasha's mother" and her introduction and character remained the same as in the manga series. The anime, however, added a few extra scenes, and showed a young Inuyasha in a lavish garden at a wealthy estate. He attempted to join the other nobles in a game of kemari ball, but they tossed the ball away and left as he went to retrieve it. Inuyasha later recalled this was the first time that he saw his mother's tears. Inuyasha was left with two things from his mother, his Robe of the Fire-Rat and her lip-coloring makeup. Inuyasha later gave the makeup to Kikyō.

In Episode 5 and 6, Jaken had the yōkai Mu-on'na transform herself into Izayoi to hypnotize Inuyasha (in order to find the location to Inu no Taishō's tomb), which worked until Kagome (with Jaken's staff) broke him out of the spell.

She was mentioned in Episode 89, when Kagome came down with a cold. It was revealed that Izayoi taught Inuyasha how to make a medicinal brew. It contained several kinds of herbal leaves and roots, along with at least three different kinds of liver. Sōta kept him from revealing to Kagome that he had used raw liver instead of dried ones like his mother did. Despite this minor difference, the medicine worked just the same since Kagome was perfectly well the next day.

She was indirectly referenced in Episode 167 by Naraku while Inuyasha's group was trapped inside the demon ogre's belly (he even made a derogatory comment about Inuyasha being born from a "weak human" and a demon before being corrupted by the jewel shard).

InuYasha the Movie: Swords of an Honorable Ruler
The Third InuYasha Movie provided us with details about Inuyasha's birth and how the Inu no Taishō died. Izayoi was the daughter of a wealthy feudal lord about to give birth to a child, an event that caused 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 could kill the Daiyōkai. Though Izayoi told Takemaru to leave in order to spare him from the Inu Daiyōkai's wrath, Takemaru admitted that he still had feelings of love for her, but that he would not allow her to give birth to a half-demon. He attempted to kill both Izayoi and the unborn child, but left before noticing that she was able to give birth alive to Inuyasha before she eventually died.

The Inu no Taishō easily overpowered Takemaru's men and rushed to Izayoi's aide, only to discover his beloved dead. Fortunately, he was able to use Tenseiga to revive her. The Inu no Taishō gave Izayoi the Robe of the Fire Rat and then ordered her to escape with their son, whom he named "Inuyasha". She followed her beloved's instructions and left. 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 collapsed on both him and Takemaru, he died along with him. This set up Izayoi to raise Inuyasha on her own.

It was also shown in the series that Inuyasha still tended 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 was shown about her both in the anime and manga, in the Third InuYasha Movie, it was shown how the Inu no Taishō loved her and so did she. She was kind with Takemaru, the man who admitted that 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 had a flashback in which his mother comforted him when some people called 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 the demon world. How she died was unknown, but Inuyasha must really have loved his mother, for he took fresh flowers to her grave every once in a while. Likewise, the only comment that Inuyasha made about her passing was that 'it wasn't her fault'. She died while Inuyasha was still a child, as another flashback showed a young Inuyasha, perhaps 7-10 years old, out on his own in the woods, and running for his life from Oni.

Physical description
Izayoi appears to have been a very beautiful woman, possessing long black hair and brown eyes. She was always portrayed in fine clothing, with a solemn yet graceful appearance.

Powers & Abilities
Expert Healer: Izayoi seemed to have some skills involving medicinal healing as she concocted a herbal medicine for Inuyasha that instantly cured colds whenever he caught them while as a child. She was skilled to have taught Inuyasha how to make one himself as he was able to brew his own that instantly cured Kagome's cold. The very fact that Izayoi seemed to have a skill like this when she was originally a human princess was impressive as well considering that as a princess during the feudal era, she would have only been taught how to behave like an aristocrat.

Relationships
Unfortunately, very little was known about the relationship that Izayoi and the Inu no Taishō had. In Zusetsutaizan Ōgikaiden book, she was, however, listed as his "wife". The circumstances that led to their meeting were unknown. However, both appeared romantically affectionate toward one another. Izayoi referred to him as and the Inu no Taishō clearly had only her in mind after his battle with Ryūkotsusei: instead of tending to his wounds, as he rushed to her side, only to find her dead and cradling their child (thankfully, he was 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 showed that 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 became very defensive when she was brought up. He preferred not to talk about her, though it is clear that he misses her a lot. According to the third movie, Inuyasha would occasionally visit his mother's grave to place new flowers. She loved and cared for her son wholeheartedly, and realized that he would have a difficult life with being a half-demon.
 * Inuyasha

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

Trivia

 * 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, had a tendency to draw noble women in a very similar manner. Izayoi's design was not much different from other characters of high rank, apart from the color and design on her kimono.
 * Izayoi was 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 made her son, Inuyasha, of noble blood on both the human and demon sides of his family as his father was the Demon Lord of the West.
 * Her seiyuu Kikuko Inoue voiced Kasumi Tendo in Ranma 1/2, from Rumiko Takasashi's work.