An Ayakashi is a special kind of Yōma, quite common, and priviledged target to Shinobi groups, that are capable of possessing a dead shinobi corpse, being an usurper kind of fighter in missions. Their name means "Yoma with an Human appearance". It appears notably in SKBR:N.
The Ayakashi does not have any proper appearance nor language, nor even expressions on their own. They first appears as desincarned entities with two red glowing eyes. It is strong and subtle, and aims to kill a shinobi or to possess a dead one to use it as a puppet.
Upon possessing a corpse, they take the appearance of that corpse, but modify it to give cat-like eyes, blood red skin, along a whole red color scheme on the outfit, and a kind of erratic behavior. It also gives to the victim some particular attacks the victim is basically unable to do. It also steals every lines the Shinobi could speak, making it a half-perfect imitating puppet of the original.
It is also one of the weakest and variable kinds, as it is dependent of the victim it possesses, which is often a lesser shinobi it render stronger and more resistant than usual, but are shown to attack both in packs or alone (when found), but it is still a highly dangerous and powerful enemy. Beating the "puppet" allows to free it from the Yoma's influence.
In SK universe, the Ayakashi, as evidenced in some TS files, is perceived as a danger more than some others Yomas because it's ability to possess a shinobi can result in leaks, leaks that are dangerous in the war between Shinobies, and the Shinobies are usually ordered to take them out to prevent those same leaks. They are themselves hard to be kept secret as they tend to be in populated areas.
The same TS files reveals that the Akayashies are actually attracted not only by blood, but also by regrets, tourments of grudge spirit, and thus one of their victim must be immediately laid to rest.
Under some circumstances, a shinobi may become a Yoma. According to the Abyssal "Campaign" in SKBR:N, if a shinobi gather too much power without being able to control it, and leave itself being overrun by it's own emotions, it will become a Yoma, and probably an Ayakashi. This is the truest for revenge-seeking shinobies who try to gather the most power they can in order to kill Yomas.
This can be favored by the use of some Forbidden Ninja Arts, like Blood Riot, what have as known side-effect the destruction of the user's mind.
In some rare cases, Kagura may intervene and open a trial in her dimension about the affected Shinobi. A trial which can lead to the immediate destruction or the exoneration of the accused.
- Ryōki : According to SKBR:N, during the event of her own death, the perpetrator of the massacre was an Ayakashi. It then possessed her, and attacked Miyabi who already activated the FNA : Blood Riot. It is defeated, but Ryouki tells Miyabi her last words to her sisters, before crumbling...
- Crimson Squad : Actually, this is not an Ayakashi, but the work of Orochi on Homura's friends. It give similar effects as an Ayakashi's possession, except it can be applied both on living and dead shinobies. Fortunately, freeing a "puppet" leave it alive, where it is at least dying with an Ayakashi.
- Miyabi : She is the main character played during the Abyssal Missions in SKBR:N, and at the end of Ryōki's death event, she loses her control. Luckily, she fight her "abyssal side", and win the trial (which was a duel), allowing her to return to herself, in comatose and amnesia.