So, first off, I'm going to explain just HOW Syd is Alias from the Gravity Rush franchise.
In GR part 1, Syd and Alias are never shown in the same frame together. Not only that but Syd has the little well known phrase in the first game and that is, "That's the spirit!" When the boss battle for Alias pops up, he says "That's the spirit, Kitten." After you chase all his clones at least.
Another way Syd is Alias is that Alias can pretend to be whoever he wants but out of everyone, he chooses Syd. Not only that but this power is never mentioned again! After Kat first encounters Alias, an information chat bubble appears at "Pandora's Fortunes." If you go there and get the conversation, you get this... Kat: "How can I find Alias?" Aki: "The Police Officer is the key." What all officers do we know? That's right! Syd, Chaz and Bolbosa! After GR2 we already know Chaz isn't Alias.
At the end of the first game, Syd seems to know who Cyenea is. Not only that, but Kat has a dream sequence in chapter 19 and afterwards Cyenea, A DREAM GUARDIAN, shows up after Alias takes of his mask in Kat's dream and Kat wakes up in disbelief.
In an early sketch of Alias, he has white hair like Syd. Notice how there is ZERO early sketches of Syd and yet many early sketches of Alias.
