I was disappointed in NG2, that Ryu couldn't use the Blade of the archfiend like how Genshin used it, but it looked like for a bit in the trailer he used it by itself. Was he using it like that, or was it just so fast it only seemed like it?
He uses it by itself. He did so in the original NG3 release, and he does so in Razor's Edge. He does not, however, use Genshin's stylish reverse-grip fighting style. Ryu uses the Blade of the Archfiend with his Dragon moveset and a few new combo branches (The Underworld drops).