The Nyanko Sisters, Shiro and Kuro, are minor antagonists in the Soul series, debuting in SoulCalibur IV.
The sisters are twins, hailing from Japan. The two notably share many features with Mitsurugi, including blood type and hometown. The two were raised to fight, raised by a group of noblemen, who feared attack by many strong men and women, who roamed the lands of Japan. However, the sisters grew too strong to be kept by the noblemen, and grew too song for their master's own desires, eventually killing them, to free them of restraints. Ever since, the two fought harder, to improve their strength, and eventually became assassins. However, rivalry grew between them, as they questioned who was the stronger.
The sisters were unaware of Soul Edge, until they were found by High Priestess Eronoru, who found them, and requested they join her, as defenders of the wielder of Soul Edge. They agreed, under the understanding that it would be like a test for them; eventually, they would battle each other, and the strongest would emerge the victor. As such, they joined, defending both Eronoru, and Nightmare. The powerful sisters battled hard, and eventually came up against each other, with Shiro, the elder twin, emerging the victor. Bitter Kuro did not accept this, but continued to fight alongside her sister. The two were later defeated by Siegfried.
After Eronoru took the Soul Edge, the sisters were still bound to her, by loyalty. Bitter about her defeat still, Kuro demanded a rematch of her sister, which she ultimately won. Shiro also did not accept this, but continued along by her sister's side. The sisters once again battled to the final stages until they eventually came up against an aged samurai, who refused to divulge his real name, only calling himself "Sedantry." The old man battled fiercely, and shockingly slew Nyanko Shiro, but was fought off by Kuro. Kuro, enraged by her sister's death, departed of the arena, and was not seen again, throughout the rest of the tournament, leading Eronoru to denounce her a traitor.
Now alone, Kuro makes a surprising return to SoulCalibur V. Her entire design has been changed, but the basic "black cat" theme remains.
The sisters are seen to have magical ability in their fighting style; they can levitate off the ground, and charge headfirst at their opponent, usually catapulting them upwards; this leaves the opponent open to any other attack. The sisters generally exploit any slight weakness in an opponent's defense, with strong attacks. They have good long range attacks; however, they are easily evaded, while their close range attacks are not as easy to prevent.
Despite being Japanese truly, the sisters are seen to be tan-skinned with deep brown hair and brown eyes. They both wear Bhast masks, shaped akin to cats, hence the name "Nyanko", "nyan" being the Japanese phonetic for "meow". The sisters are akin to a palete swap, with 1 costume each; Shiro, the elder, is dressed entirely in white battle gear, hence the name "Shiro", meaning "white". Kuro is dressed similarly, (although skimpier) in entirely black battle gear, where the name "Kuro" comes from, meaning "black".
In SoulCalibur V, Kuro returns alone. While before she fought with a bhast mask, she now fights blind, with a mask covering her eyes, and cat ears atop. She wears a tear-styled top, black leggings and stiletto heels, with a chain around her waist and scissor claws, reminiscent of cats claws. As usual, her entire theme remains black.
Slamming the opponent to the floor first, the chosen sister throws her opponent into the air, using her swords, and then teleports above her opponent. She then shoots a soul-charged bullet into the opponent, sending them crashing into the ground again. The selected sister then stands triumphantly over her opponent.
The sisters only lend their name to Soul Edge by loyalty to Eronoru, after being asked to defender Soul Edge and its wielder. However, the two express interest in Soul Edge, itself, suggesting they could be relegated into "evil".