Now that Yaiba is behind us, let's get back to the NG4 discussion:
I think Team Ninja really felt the stab with Yaiba's reviews and they are getting emotional on Facebook, so we can probably expect a killer app out of NG4 because they feel like they have something to prove at this point when it comes to the NG series, and I would agree with those feelings.
Hayate:
He exists in DOA to show us that ninjas are not invincible. He has amazing moves just like all the other ninjas, but mentally he is not even close to being as strong as: Ryu, Ayane, or Kasumi. He got amnesia from being tested on, demons can fuck with his head, and he was also destroyed by Raidou. Literally man-handled. Kasumi killed him.
I think he could be a great addition in some regard. He could try really hard on a mission, and comes close to dying, but Ryu comes and saves his ass in super ninja fashion. That would be cool. If he is in Ninja Gaiden, I hope he's crazy, and not a cookie-cutter character. I want thought going into him. And I don't want him to take the spotlight from Ryu at any point. He's Ryu's bitch as far as I'm concerned.
Flock of Tengu:
I want more Tengu bosses, but for Ryu to face. I thought the Tengu Brothers were quite a fun addition to Sigma 2, and I would like for Ryu to fight a flock of them. I think they should be a little more unique than the twins, but it could be a very cool boss addition if done correctly.
Rachel:
Since Rachel is the most popular heavy by far in DOA, and since she is so damned bad-ass and amazing and has been a victim of a lot of love recently, I think she should definitely be put into Ninja Gaiden 4. I want to see her wreck fiends. Sometimes there can be too much ninja, and I think she also can balance the roster out.
Soundtrack:
I think that one thing Ninja Gaiden games haven't really brought to the table is a killer soundtrack. I mean Black and 2 had some good ones here and there that I remember by memory, but not like God of War where I remembered a lot, but felt it when I was fighting.
Ninja Gaiden needs to work on that a little. Good, thrashy, grungy heavy metal would fit Ninja Gaiden in some sections of the game.