The Ayakashi sisters worked under the direction of Rubeus; each of them has powers centering in a specific medium. He sent them to neutralize the senshi. Each of the sisters has an upside-down black crescent on her forehead, the symbol of the Black Moon; they also wear the dangling earrings of the Black Crystal, which hold negative energy. One by one, they visited the past and targeted a Sailor senshi. They are (in order of appearance) Cooan, Beruche, Petz, and Calaveras.
"It's all right; don't be sad. Everybody dies." - Cooan, Act 14
The youngest of the Ayakashi sisters is the strong, radical Cooan. Her hair is long, black, and done up in two pointed balls on top; in her normal form, she wears a striped outfit with a frilly tutu and has a round jewel on her forehead above the black crescent. Her powers lie in the medium of fire. When she went to the past, she burned people to charred crisps with only a gesture; the many incidents of seeming spontaneous combustion attracted Rei's notice. Calling herself Kurozuki ("black moon") Cooan, Cooan pretended to be a student at T-A Private Girls' School who was interested in supernatural studies. At the festival at T-A, she set up a fortune-telling booth to compete with Rei. By predicting that her clients would soon sicken and die, she threw the festival into chaos. Rei and Kotono ran to find some nuns to restore order, but all the nuns were actually droids, and one of them spontaneously combusted.
This was too much for Kotono, and she fainted. Rei was much sturdier; she transformed into Sailormars and blasted the droids, upon which Cooan revealed herself. "I'll fight prophecies with prophecies," she shouts, "and fire with fire!" She blasts fire from her hands, and it surrounds Rei, seizing her. Scorched and hurting, Rei was unable to act. Even when Sailormoon destroys Cooan with "Moon Princess Halation," the fires around Rei didn't stop. Rubeus came out of nowhere and claimed Sailormars, laughing as he disappeared.
"I will remove the obstructing game piece." - Beruche, Act 15
The third of the Ayakashi sisters is the determined, analytical Beruche. Her hair is long, pale blue, and woven into a long braid that wraps once around her head before hanging down; she wears a tight white/blue outfit that leaves nothing to the imagination, and thigh-high boots. Her powers lie in the medium of water; when Ami used her mental sensitivity to discover a leaky pipe, Beruche thought it was improper that Ami didn't even use a pendulum to dowse for the leak.
She challenged Ami directly, going on TV as the famous dowser Miss Beruche. She announced to the world that she wanted to compete with the genius-girl chess champion Mizuno Ami, at any cost. Ami confronted her at the World Chess Tournament, and was shocked when Beruche addressed her as Sailormercury. Ami transformed and flung "Shine Snow Illusion" at her, but Beruche surrounded her with water. The liquid rushed into Ami's eyes and poured into her mouth, choking off her air. The water did not subside, even when Sailormoon killed Beruche. Rubeus appeared and took Mercury away in a bright flash of light, while the stunned senshi stood by.
My thanks to Ian Miller, who informs me that the name "Beruche" is the Japanese approximation of the French name "Berthier."
"Everyone here... they won't live much longer. It's time for the droids to replace them." - Petz, Act 16
The eldest of the Ayakashi sisters is the fierce, vengeful Petz. Her hair is black and short; she dresses in a very low-cut tight black outfit, and high boots. Her powers lie in the medium of storm, which makes her the opposite of Sailorjupiter; she also looses a cold virus upon the city which infects Makoto (among others). She also caused many crop circles.
Petz didn't even bother to confront Sailorjupiter directly. She just loosed a virulent cold upon the city of Tokyo, and followed it up with fierce thunderstorms, one after the other without a break. She also created a droid in Makoto's exact image, and sent it to attack the real Makoto. It leapt into Makoto's apartment and started throttling the girl. Sick and weakened, Makoto was nevertheless able to defeat it by transforming into Sailorjupiter. As Jupiter, she then seized her duplicate and threw it to the floor with such force that it turned back into a droid.
Sailorjupiter then sought out Petz, and threw "Flower Hurricane" at her. Petz cried back, "Your hurricane is of that level? Watch - the earring of the Evil Black Crystal can call a tornado!" Holding out her hands, she summons a fierce storm. Electricity crackles around Makoto, shocking her; she screams in pain. Usagi and Mina finally arrive and Sailormoon blasts Petz away; however, it is too late. Rubeus seizes the suffering Jupiter, and they fade away.
"This is the birth of the cosmic millennium; this is a time of change." - Calaveras, Act 17
The second - and last to die - of the Ayakashi sisters is the sensitive Calaveras, of the spirit medium. Her hair is tied back with a bow, reminiscent of Minako's hairstyle. As she is brooding over the deaths of her sisters, Rubeus comes up and kisses her on the shoulder, reminding her that she has a mission...
As the channeler Miss Calaveras, she becomes famous as someone who can connect to the spirit dimension. She convinced her audiences that medicine and hospitals were untrustworthy, and that they should accept no one else's control. She told them that they should not trust the bright moon, and that when the people of the Black Moon arrived, they would bring salvation. Mina saw this as a direct challenge to Sailormoon, and busted into Calaveras' public channeling session just as Calaveras was convincing her audience that they needed to destroy the ginzuishou and the Sailor senshi. As Sailorvenus, Mina denounced Calaveras as a fraud; Calaveras responded by summoning the spirits of her sisters. With "Spirit Energy Attack!", energy enclosed Sailorvenus. Mina shouted her defiance, but felt her body beginning to disintegrate... luckily, Sailormoon got there in time and defeated Calaveras. Since Tuxedo Kamen had injured Rubeus just moments before, they were able to rescue Sailorvenus without fear of intervention.
Calaveras was the only one of the Ayakashi sisters who was unsuccessful in capturing a Sailor senshi for the Black Moon. Personally, I think it's because her power and Venus' power are not in direct opposition. If you look at the other matches, you'll see a pattern: Cooan matched Rei prophecy for prophecy and fire for fire; Ami and Beruche fought on the dual fields of chess and water; and Petz and Jupiter attacked one another with storms. Calaveras, on the other hand, spoke with the spirits of the dead while Venus' powers are concentrated in beauty, love, and metal.
I suppose you could make it a stretch and say that Calaveras was spreading hate while Venus spreads love, but the connection is not as solid as the connections between the other Ayakashi sisters and the senshi. This unequal match is, in my humble opinion, why Calaveras was unable to neutralize Venus as fully as her sisters defeated the other senshi.
The person that Calaveras should have taken on was Chiba Mamoru. Mamoru-kun spoke to the spirits of dead people on a regular basis; he communicated with his dead generals through their gemstones. His power of psychometry also lets him feel the spirit of whatever he's touching. If Calaveras had challenged Mamoru, I would've bet on Mamoru; but at least their powers would have been matched.