My point with Ryu Hayabusa was that his father appeared as the main character in the first Ninja Gaiden games. It was only later that Ryu came into the picture, and would become the main character in the reboot. Look at how popular Ryu Hayabusa is.
I don't know what you're talking about, it's always been Ryu that you played, even back in the Arcade and NES games.
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And while your point of Taki being popular because she developed over the games is true to an extent, replacing her with Natsu was completely unnecessary. She brings absolutely nothing new to the roster design-wise, she's just a younger and more annoying Taki. At least Xiba is a whole new design, and Xianghua moving like a teenager even though she's in her 40's wouldn't make an ounce of sense, but Taki could have very easily returned with Natsu's style, which is just SCIV Taki on steroids. Project Soul thinks that Natsu would make the game appeal to younger audiences, but this is ridiculous and just comes to show their lack of understanding of their audiences. This game's younger audience fits in one of these three categories: Anime fans that like hyper-masculine fantasy designs like Nightmare and Astaroth, kids that play for the character creation, and pervy 12-year olds that play for the boobs. Thus, the only logical reason for the removal of Taki in favor of Natsu is effectively destroyed.
As for your claim that it's pure nostalgia, I'm gonna have to say no. If it were nostalgia I'd be complaining about characters that I actually cared for, like Cassandra or Hwang. Not having Taki is just about the same as not having Mitsurugi or Ivy, or having a KoF game with no Mai.
I get what you mean, well maybe not completely remove them, but do you really think they need to appear in every signal game in this series? As I know Kan or Ryu or Chin Li etc. does not appear in every game too. What I mean is that you need to give those newer characters more chance to be in the game, I also think it is pretty weard that they deleted both old and new characters ( not really new characters but characters that were created later in the series ) in SCV, and they only made a few new characters. I think this is why people are mad about this game.
Ryu and Ken have been in every single game of their series, and Chun Li was only absent in two games (one of which was an update of the other). And yes, many people were mad because their characters were gone, but continuing to ignore these removed characters even though they evidently had a significant following isn't the best way to go for a series that caters so much to the casual crowd.
Cassandra was created later in the game, but I think she's also an iconic. Same thing as Talim, Amy or Zasalam or Rapheal. Old characters are iconic, but that does not mean new characters can't be iconic. My first soul calibur game was SCII and the reason me and my friends would play that game is we got attracted by Cassandra, that makes us want to play the game. And until now she is still my favorit character ( I didn't play SCV because she is not in there ). Other of my friends would play this game is because they like the character Setsuka from SCIII and some other new characters. So new characters can also be important and can also be iconics. So we should keep the in the game and make them appear more in the game not getting ride of them.
To me, anything created up to SCII is iconic to this series.
And this illustrates my point perfectly, people: This is an example of a casual follower who gave up on the series because the characters they liked were removed/replaced. It's not an attitude I condone, but it is more common than it should be.