Yomi Isayama

Yomi Isayama (諫山 黄泉, Isayama Yomi) was a major villain who was introduced in the first story arc of the manga. She was the sister-figure of Kagura Tsuchimiya who turned evil because of the power of the sesshōseki. She was the person responsible for killing Kagura's father. As a living human in the past, she was extraordinarily talented and fights with her spiritual beast, Ranguren. She slaughtered over 70 ministry agents by herself and defeated the head of the Tsuchimiya clan and his spiritual beast, Byakuei. Later, She was then killed by Kagura herself and has turned completely evil in her afterlife. In the first arc of the manga, she becomes even more powerful as an evil spirit. She tries to awaken a great demon sealed in Tokyo, and seals a piece of the sesshōseki in Kensuke Nimura. For this, she incurs Kazuhiro's wrath, and he takes away her own sesshōseki.

Appearance
Yomi is an attractive girl of medium height, possessing purple eyes and jet black hair that is as long as her waist and falls down over her forehead in a trimmed fringe. In the anime, just like Kagura, she is shown wearing her black and white school uniform most of the time, even donning it during her Vanquisher duties. Towards the end of her life her uncut Bane Stone could often be seen glowing in the middle of her forehead, signifying moments at which Yomi was in control of her own actions.

After her death and subsequent resurrection as an evil spirit, Yomi's appearance became far more demonic in nature, with serpentine eyes, the Bane Stone permanently visible on her forehead and sharpened teeth. She no longer wore her school uniform in this state, instead almost always wearing a kimono and carrying a parasol on her person.

Background
Yomi lost her parents at a young age to specters, and was saved and adopted by Isayama Naraku, then head of the Isayama family. Yomi grew to love and respect her foster-father, and polished her skills to repay him for his kindness, becoming one of the most talented warriors on the planet and something of a prodigy among the Vanquisher clans due to her ability and young age. Her efforts led to her inheritance of the prized Isayama heirloom, the sword Shishio, which held the spiritual beast Ranguren in it. Much like how Naraku adopted her into his family, so did she adopt [Tsuchimiya|Kagura Tsuchimiya] into theirs, treating her as a little sister and offering her love and friendship throughout their teenage years. Before Naraku's death, she was betrothed to Izuna Noriyuki and would have succeeded Naraku as the next Isayama head. However, Naraku's death at the hands of her cousin Mei, who was jealous of her good fortune, and the alteration of Naraku's will, resulted in her being stripped of her position in the family and therefore her entire inheritance. Yomi eventually found out the truth behind her father's death, revealed by Mei herself after the latter lured her out in order to kill her. Partly in self-defense, she killed Mei and avenged Naraku, but was ambushed by Mitogawa Kazuhiro, who wounded her so badly that she became hospitalized, her throat and most of the tendons in her body cut and unrepairable, unable to talk or move. This, in addition to the suspicion that she had murdered Mei, led to a series of events that caused her to succumb to Mitogawa's temptation to accept the sesshōseki, resulting in her transformation into an evil spirit and subsequent rampage; she went on to kill over 70 Ministry of Environment agents, as well as several Ministry of Defense units single-handedly, and even mortally wounded Garaku Tsuchimiya, head of the Tsuchimiya family, in combat. She was finally stopped by Kagura, who slew her big sister in tears and allowed Yomi to die peacefully with a smile, telling Kagura she loved her and putting her spirit to rest.

However, the power of the Bane Stone would later resurrect her as a demonic entity once more, and she would go on to come into conflict with Kagura several more times.

Abilities
Yomi was an extremely powerful and talented warrior, with speed, strength, agility and durability far surpassing that of an ordinary human or Ministry agent. Her speed was such that she could move from one location to another so quickly it appeared as if she was teleporting, deflect bullets with casual ease, and move across rooms faster than armed gunmen could react to her. She was capable of cutting through large Category B spirits with great ease using her sword, suggesting an immense level of physical strength. The highly skilled and capable squad of Seers, Section 4 of the Paranormal Disaster Countermeasure Headquarters, were slaughtered by Yomi with the utmost of ease in a matter of seconds.
 * [Ranguren(乱紅蓮)/Nue (鵺) ]: Yomi's (Ranguren) familiar, bestowed upon her by the Isayama family heirloom, the mighty katana Shishio. Ranguren is a large chimera possessing great strength and ferocity, along with the ability to fire a "Roar Wave" of destructive energy from its mouth with enough power to practically annihilate city streets. Nue can also fly, as can Yomi when in her familiar's proximity and the Spirit beast is sealed in the sword (katana).
 * "Phantom" The Death Stone (Bane Stone): fragments of soul belongings to nine tail foxes, crystallized forms of pure supernatural energy, whoever possesses one will be granted limitless spirit power as it devours their soul alive and turns into a  phantom . Then they'll synchronize with the nine-tail foxes hatred and attempt to destroy everything in existence. Yomi acquired the stone from Kazuhiro Mitogawa by accepting the hatred, yomi granted self-regeneration ability . Kazuhiro Mitogawa puts the stone in the forehead of yomi for symbolized that she accepted it. During the fight the stone glows bright red in yomi's forehead, the stone gave yomi strength and stamina into the fight. The stone appearance is a oval shape and red color.

Yomi initially met Kagura when they were both children after Kagura's mother was killed and her father was called away by his Vanquisher duties. Yomi immediately took to taking care of Kagura as if she were her own daughter, insisting to her father that Kagura move in with them and doing everything in her power to eliminate sadness from Kagura's life. By Yomi's own profession, she had always wanted a baby sister to care for and look after, and with Kagura taking this roll formed a deep bond with her. The two were practically inseparable, and became closer to each other than they were even their own parents and blood relatives. When they first met, Yomi recognized that Kagura was grieving and in pain following the loss of her mother, and felt a strong desire to make her happy and protect her by any means necessary. She often advised and sympathized with Kagura during difficult times, cheering her up however possible and making things as comfortable as she could for her. Their feelings for one another were so strong that they genuinely considered themselves sisters, and each would do anything to make the other happy. Yomi's adoration for Kagura often resulted in the latter's embarrassment, however, as Yomi proved unashamed at frequently fawning over, hugging and even kissing Kagura at home and in public.

After Yomi was attacked by Kazuhiro Mitogawa and hospitalized, rendered immobile following over a hundred nerve and tendon lacerations and mute after her pharynx was crushed, Kagura stayed at her bedside to take care of her and comfort her however she could. After Kagura started crying and lamenting why this had to happen to her sister, Yomi showed the depths of her will and love for Kagura, moving of her own volition for the first time in months to stroke her head with one of her injured hands. However, Yomi's strong attachment to Kagura proved to be her initial undoing: after Kagura fled the room in confusion when she learned Yomi had killed Mei without knowing of the details, Yomi, crying and trying to call her back but unable to because of her vocal injuries, was approached by Kazuhiro, who used a Bane Stone to forcibly begin healing her damaged nerves, causing her horrific pain. Confused, angry, depressed and in agony, Yomi allowed the hatred in her heart to take control of her and embraced the Bane Stone, becoming an evil spirit.

However, these were by no means the most powerful emotions in Yomi's heart, and her real self actively fought for control and expressed abject terror at what she was doing as a spirit, even attempting to commit suicide at one point and finding she was unable to. Eventually her fight to control the Bane Stone proved ultimately successful, as she forced the Stone to accept that the strongest emotion in her heart was her love for Kagura and her one true desire was to protect her, and she ultimately wrested back control of her actions long enough to allow Kagura to mortally wound her. As she lay, dying, in Kagura's arms, even then Yomi attempted to comfort and reassure her to the best of her ability, professing her love for Kagura and telling her how proud she was of her before dying peacefully.

Noriyuki Izuna
In the anime, Yomi's father set up an engagement between her and Noriyuki when they were young, arranging a marriage to join the two's clans together. After Yomi was suspected of murder for killing Mei Isayama, hospitalized and stripped of her inheritance after the murder of her father, Noriyuki's father cancelled the engagement, much to Yomi's grief, and because Noriyuki never even came to her room to visit her this caused her to sob due to loneliness, contributing heavily to her acceptance of the Banestone and corruption. It is shown in the anime that they didn't really get along most of the time, as Noriyuki was rude and insensitive about Yomi attempting to wear perfume to impress him, frequently flirted with other women in her presence and even hit her back after she slapped him (though Yomi proceeded to hit him back even harder and incapacitate him), and often spent more time playing darts with Kazuki Sakuraba than with her. Yomi was frequently paranoid and suspicious of him, and quick to anger at him whenever he annoyed her. However, they agree to try and get along for the benefit of Kagura Tsuchimiya and both their families, and are seen enjoying each other's company later on in the series. Although Yomi may not actually love Noriyuki, she is willing to comply with the arranged marriage out of respect for her father, who she feels she owes everything to. In the manga Noriyuki didn't want Yomi to die yet again, so he gave his life protecting her.

Etymology

 * The name Yomi means "yellow" (黄) (yo) and "fountain, spring" (泉) (mi).
 * Yomi's surname Isayama means "admonish, dissuade" (諫) (isa) and "mountain, hill" (山) (yama).