I will try to give to the thread the most exaustive answer possible that I can give me too, even for claryfing some of the things that I read:
But who's to say Nyo isn't Ayane
•Nyotengu means female tengu, Ayane has been dubbed "The Female Tengu" in the past
The reasons for Ayane being nicknamed Female Tengu are found in the original manual for DoA2.
I wasn't able to find the folder where I saved scans of the DoA2 Hardcore manual, by the way I'm pretty sure that her profile should be basically the same (at this link you can find the official DoA2 site in English where you can read her profil basically unalterated:
http://www.dead-or-alive2.com/ )
Here her profile from the DoA2U manual:
So in all the versions it's said as Ayane got her nickname related to the tengu race because her fighting style with the ninjutsu was judged deadly just as the one of the mythical creatures. It's not something fundamental for your theory Ayane=Nyotengu, but for being precise I think that it's important to notice how the scene at the end of Ayane's DoA2 story mode wasn't the one to give the birth to a nickname from the fans, but rather a scene directly tied with the official nickname and infos given in her background. Indipendently from the translation used, the meaning of that scene is Ayane showing us that she was able to beat Bankotsubo just as in quality of being a tengu herself (of course one of their race only in a metaphorical way) and so on par/superior with a real tengu.
But why only Ayane is considered a "tengu" and not for example Kasumi or Hayate that are of course deadly ninja too? The game never say this more clearly of what it's written in the manual, but I've always supposed that this could be realized from the informations given us on the Tengu race (added in an extensive way since the manual of the DoA2 PS2 version):
EDIT: If clicked the DoA2 manual pages will appear zoomed
In the underlined parts of the text, you can read 2 main basic infos about the characteristics of the tengu race that are then implemented in their fighting style:
- They have an extreme agility indipendently from their possession of wings, something that allow them incredible feats as not ordinary jumps, something comparable to the feats performed from the ninja as part of their training.
- They posses magical "technologies" at the basis of Japanese occultism, considered god-like powers
Now with the development of both DoA and Ninja Gaiden series, we have seen great feats under both the aspects from all the shinobi characters acting in such games. But if you think to what we got with Doa2, made perfectly sense to attribute such characteristics to Ayane rather than Kasumi or Hayabusa.
- About the first point, Ayane was surely the shinobi more agile in the game (and in some extents I would say that is still the one in DoA5U rivaled from Momiji), overall with all her spins, possibility to change side and to reach the back of the opponent in a very fast way. Ryu with his Izuna and Kasumi with her teleport had surely something to say about, but if I should misunderstood he agility of a character with "flying", in DoA2 for the most of the time that would be surely Ayane's one.
- About the second point, we have to remember that until DoA3 the only ninja that we saw performing naturally magical attacks (later called "ninpo") was just Ayane with her alternative secret ending of her match against Kasumi. Even this thing is not coincidential because it's again the same manual of DoA2 (see the page below) to say us how Ayane's Hajinmon sect is gifted with secret magical techniques that are owned only from them (while the Tenjinmon clan is more oriented toward the improvement of physical skills). At the point that appear strange to think that the Hajinmon is a sect of shinobi that follows loyally the Tenjinmon rather that being on par with it:
•Nyo more or less resembles Ayane's moves with her 2H+K 3x
If there are really similarities between Ayane and Bankotsubo/Nyotengu movesets, I suppose that this should be something done having in mind the resemblance between the fighting styles as stated in the original DoA2 manual (that I explained over).
•Nyo and Ayane are tag partners in command training. Why not Rachel? She hunts fiends but still, Ayane of all people?
This happened not only for the relationship between the two characters as put from the people behind the game, but I believe overall because the fans of Ayane showned to like very much the idea to think to the kunoichi as a female tengu. Her official nickname was used for years from her fandom, Japanese too I believe.
This was the reason because:
- DoA Dimensions, even creating a new canon for the series, kept alive the tie between Ayane and Bankotsubo (Genra's trick or less, Ayane was intercepted from Bankotsubo after her fight with Kasumi in the storm, and I always remained of the idea that Bankotsubo was directly controlling her (just as when she was brought in his orinical illusion)). Even if this is just a brief part of Ayane's role in the plot, paradoxically this make her tie with the tengu even more strong than in the original timeline (where the scene of her talking after the defeat of the tengu is always been not canon how in DoA3 was stated that Hayabusa was the man to kill Bankotsubo, making so of his DoA2 ending the real one).
- Ayane got a reference to her nickname even inside the Ninja Gaiden Clans game, with her depiction in this tengu themed outfit (and seeing the card it's possible to realize how Nyotengu's mask is actually inspired to the one used from Ayane in this outfit, but again there is no secret meaning beside this):
- Finally, with DoA5LR Ayane ended to be put in tag with a real female tengu, and what it's now only a tag team can be surely seen as an anticipation of a relationship between the two characters even in the plot of the next game (where Nyotengu will get an official role in the story making canonically her appearence in it).
On a sidenote, I don't consider the interest of the fans for Ayane's "definition", and the consequent impact on the series with Nyotengu, something different from what happened with Bankotsubo's mantra
"Everying is my deception". Even if being his main sentence repeated with all the characters in the DoA2 story mode, that line remained confined to that only game. Not being neither included in Bankotsubo's DoA4 (I hope to not remember bad), make me think that the importance of that line was realized only from the fans of the characters and neither from the developers (that recreated the same scene with it in Dimensions just as a parallel with the events of the original DoA2).
I'm of the idea that only the recent tam-tam on the social networks for the return of the Bankotsubo in the DoA5U roster, using that sentence as spot for him, was able to make realize to the developers the impact of that line on a part of the fans. This is the reason because they thought to associate the April's fools day with this line (I still think that was a stroke of genius from them), to announce Nyotengu just using this sentence in their messages, and to assign to her this as one of her outro, not randomly hearing the voice of Bankotsubo just in the background of this sentence. Bankotsubo is not returned but his line will remain forever in the series associated with the tengu (and not only with his character) and IMO this was made possible just from the behavior of the fans. Who say that fanservice in DoA means only showing in a sexy way the female characters?
•Nyo is 1018 years old. Random number? Ayane is 18 years old as of DOA5U
I suppose that you are saying this with using as basis the other hints (because the simple age alone wouldn't be alone for stating that one character is another, even because we have already other 18 years older characters in the roster).
The explanation for the name 1018 is very likely what other users have already said, this is an hint for the players to consider Nyo as a girl of 18 years (or with a tengu age comparable to the one of a human 18 years old). I agree with you that Nyoengu actually give the impression to be more older in his twenty, but one of the sexy clichè in the Japanese fictions is to create young characters with big breasts (see for example the Senran Kagura series), so to think to a girl of this age with a such developed body is used to make her sexy for a part of the audience (same thing that happens with Honoka).
•Raidou is Ayane's father. She is half demon? She has evil energy in her?
I don't know what to say about Raidou because at this point we need of DoA6 for realizing exactly what is the source of his powers. In DoA Dimensions Irene analyzing the data provided from Ryu, get the conclusion that DOATEC is
"experimenting with DNA sequencing, trying to recode genes to boost the human body's physical power". Hearing these words, Ryu put them in relation with Raidou's over-strenght and the revealed clone of Kasumi.
So it's confirmed that Raidou allowed experimentations from DOATEC (through Donovan or Fame?) for increasing his skills, and very likely this explain the reason of his red aura released from his body (not a case that it's pretty similar to the same thing that happens with the bodies of Alpha-152 and Phase 4), but it's not clear how much of his abilities at the time of DoA1 were natural or the outcome of these experiments. Even his ability to steal the moves of the fighters copying them through the eyesight is shrouded in the mistery, from what I know it was never explained if he trained in it or obtained it with DOATEC (I'm just sure that no one in the Tenjinmon clan owns it, whatever this can means: being a prohibited Tenjinmon ninja tecnique, being a technique not known from the Tenjinmon clan, or not being a ninja technique at all).
Now with Honoka we got a character that possess in some extent the same characteristics of Raidou (the aura from the glow and the stealing skill), and apparently could be related to him. If she was her daughter this could indicate that she got such characteristics from his father through the brith (shouldn't be strange that Ayane not posses them, after all not everything from the parents is always passed to each son), but again this alone doesn't explain if Raidou has always owned them or less.
But putting aside this speculation on Raidou, your assumption start from the fact that you associate the tengu race with evil energy. Actually it's not so, in the DoA folklore they aren't evil creatures, just mythological ones that live separated from the humans and that can also teach them things. Bankotsubo is clearly indicated from the story as a villain even for his race, someone that used his powers for assassinating their leader and that then passed to the world of the humans for bringing destruction even on the Earth (according to the orginal timeline, however the part of him being a criminal and killing his leader remained intact even in the new canon setted from DoA Dimensions)
If Nyo was simply a female tengu come to avenge Bankotsubu. Then why is her name simply "Female Tengu"?
First because the nickname Female tengu is not something random for the fans of DoA and in particular of Ayane (so being something addressed to this particular part, I find just obvious to get further interaction with the purple kunoichi) and this for all the things said over.
Another possible speculation is that the original tengu character of the game, Bankotsubo, it was actually called tengu in the game, so identified with the name of his race. I suppose that to do the same with this new tengu woman, so using a generic name instead than her proper one, want be a tribute/reference just to Bankotsubo, the original tengu for the series.
