Beni

"With this rouge, I become Beniyasha, Destroyer of Lands. Tremble before the bloodthirsty dawn! Bear witness to your end, if you dare!"

- Moroha using her Beni

The is a cosmetic product used to apply color to the lips. The quarter-demon Moroha can temporarily transform into Beniyasha by using her rouge which also gives her the memories of her late dog-demon grandfather. Decades ago, it was originally given to Kikyō as a gift by Inuyasha, but was later destroyed by the shapeshifting demon Naraku when he had posed as Inuyasha, in order to kill the top-level priestess Kikyō, with the claim that such an object did not "become her at her" and that demon blood was good enough for her.

About fifty-four years later, Riku had somehow managed to find its fragments and presented it to Hōsenki II, who had it successfully reconstructed for the apprentice demonic jewel-maker to effectively create another Black Pearl for Inuyasha, who scornfully rejected them both with the claim that he could do whatever he wanted with his the keepsakes of his deceased human mother.

History
In the anime, Izayoi is shown to have been born in a wealthy/noble family and possibly used the rouge to present herself on formal occasions. After her death Inuyasha kept his mother's rouge as a memento, along with the Robe of the Fire-Rat. Some time later, Inuyasha would gave the rouge to his first love Kikyō as a gift. The rouge was later crushed by Naraku when he struck her down.

Inuyasha's and Kagome's only daughter Moroha currently holds a rouge that gives her the ability to transform into Beniyasha. According to Myōga this rouge was given to Izayoi by Tōga and have a unique property. Moroha also stores the Red Rainbow Pearl she obtained from Tōkotsu inside her rouge compact.

When Moroha was trapped in a dream during the fight with Yotsume, it is shown that Kagome had to tearfully pass Izayoi's rouge as a parting gift to her infant daughter in an unknown incident involving herself, Inuyasha, Sesshōmaru and Kirinmaru.

It was later revealed that after Naraku destroyed the original rouge, it's fragments were gathered and made into a new one, which contain Izayoi's tears of grief for her husband's death, so that Riku had the Yōkai jeweler Hōsenki II use it to create the Black Pearl, the later which can create a path to Tōga's tomb.

Physical Description
The rouge appears as a red thick cosmetic cream stored inside a white scallop shell compact that has a tiny red bow tie decoration at its beak.

The red Rainbow Pearl could be seen inside Moroha's own remade shell compact until it was scattered throughout the feudal lands by Kirinmaru in the first season finale.

Demonic Properties and Skills

 * Demonic Transformation: When Moroha applies it, Myōga had stated that "Tōga's memories are revived in her blood", and she becomes Beniyasha, therefore gaining access to her own dog-demon form as her father had in dire situations. Its full strength is yet to be unleashed. This temporary evolved demonic form is known as "Beniyasha" which could mean "demon spirit of the rouge."
 * Skeleton Melting: Beniyasha emits an aura that is strong enough to disintegrate bones like Jakotsumaru's red skeleton guards (except for his father).
 * Demonic Ability/Power Augmentation: The demon blood of Tōga amplifies his youngest granddaughter's natural abilities to greater levels but only for a few moments. It increases her natural superhuman strength, agility, speed, durability, and reflexes, and makes her fangs and claws ten times sharper than normal; a feat that Kirinmaru admires. At one point, her Crimson Dragon Wave technique had been magnified to the point that became somewhat larger and brighter, and strong enough to obey to Moroha's strong will alone. However, this advancement could only have happened due to Tōga's powerful essence aiding her and not from her evolved Beniyasha form. Since that battle, she is able to keep that evolved demon form for a longer period without fainting which she calls the "new-and-improved Beniyasha." She can now freely utilize her strengthened Crimson Backlash Wave without her the need for her enemy to geenrate a strong wind/air or demonic energy-based attack.
 * Demonic Energy/Essence Projection: At one point, her blood-red demonic aura takes on the fiery orange form of her late paternal grandfather's humanoid form, further magnifying her enhanced senses and her demon sword's two known Crimson Dragon attacks twenty times greater. It could have been Moroha's own vortex of drastically enhanced demonic energy combined with that of Tōga's fiery essence (in the form of his human-like appearance) that resided within the soil of where he had perished two centuries and fourteen years prior.
 * Memory Absorption: While keeping the red Rainbow Pearl that Moroha had taken from the deceased Tōkotsu inside, the said compact shell then pooled the memory of its original owner into the Red Pearl.

Trivia

 * It is customary since ancient times for women (at first for noble women, later for common women as well) to use cosmetics, including lip-coloring makeup.
 * In "Kagome's Instinctive Choice," its final appearance in InuYasha is seen in a memory-dream by fifteen-year-old Kagome, as she is attempting to heal a fatally hurt Kikyō from Naraku's miasma. Kikyō had taken it out and was just about to apply the late Tōga's pure dog-demon blood to her lips, but was brutally hurt by the newly born shapeshifting demon Naraku, who had had casually crushed it into several fragments while posing as Inuyasha.
 * Kirinmaru expresses his respect for Moroha's natural dog-demon abilities and strength when they are increased somewhat from her applying the pure demon blood of her late paternal grandfather, but is amused that she is incapable of maintaining such a powerful and deadly demonic form for longer than a few moments.
 * It is in the title of Episode Nineteen but it is never seen or mentioned by Moroha even once.
 * Kirinmaru is impressed and intrigued at it granting Moroha greater demonic strength from the late Tōga's blood and memories.
 * It had put Moroha on the same power-level as Setsuna, whose demonic side was just released due to Zero's intervention, but then Setsuna had overpowered her in nearly ten minutes. Moroha had referred to applying the demon blood to her lips was a way for her to "go all out" against much stronger adversaries, even that of her own paternal half-cousin Setsuna, who was under the influence of her demonic self at the time.
 * In the finale of the first season, the shell compact is not seen but is mentioned by Moroha. Also, the pure-blood demon blood of her grandfather that enables her access to her own innermost demonic self is shown on her lips as she battles Kirinmaru to avenge Setsuna's demise.
 * Moroha opens and looks at the shell rouge as the shadowy forms of her long-lost parents, Inuyasha and Kagome Higurashi, appear on her right in the first few seconds of the second season's first opening song ReBorn.