User blog comment:Master Sima Yi/Assassinews 12-05-'15 — Assassin's Creed: Syndicate has been revealed!/@comment-5174994-20150515163522/@comment-5174994-20150515222016

You're right, Abel. I'm still trying to get used to the name, as Jason is more common for me.

And no she isn't a side character. At least that's not how they're describing her. Every official source has said "two protagonists", never once prioritising one over the other, Hijo.