is one piece episode 857 filler?

Luffy manages to hit Katakuri while in Gear 4, sending him rocketing into the wall. Seizing the advantage as he continues assaulting the Sweet Commander, Luffy states that he has figured out Katakuri's powers.

He remembers the beginning of his training on Rusukaina, where Rayleigh explained the abilities of Observation and Armament Haki. Luffy has realized now that there is nothing out of the ordinary with Katakuri's Devil Fruit; the Sweet Commander had simply been using his Observation Haki to move his body out of the way up until now, and now that this has been nullified, his strong Armament…