'One Piece' episode 773 'The Nightmare Returns - The Invincible Jack's Fierce Attack' features the events that will ultimately lead to a huge battle between the pirate alliance and Kaido's powerful fleet. Episodes before 773 already revealed Luffy's plan to save Sanji at Whole Cake Island and to battle Kaido when he returns by forging alliance with other groups. Luffy's men are trying their best to prepare as they wait for the whole group to converge.

Anime News Network said that episode 773 was more of getting everything straightened out as they prepare for the ultimate battle against Kaido. Cat Viper in particular, is trying to contact Marco since he would surely be willing to fight with them. The group hides out in Wano and waits till everyone is present before they attack.

Other Straw Hats that did not stick around the previous arc like Brook, Chopper and Nami, have also expressed their support for Luffy as he goes to Whole Cake Island. There are rumors that before this much-awaited battle, an episode dedicated to the group's reunion could happen in Wano. It has been a long time, and possibly hundreds of episodes ago, since the entire crew was together. This event could be the reason for their untimely reunion.

Fandom mentions that this is the episode where Jack returns and wants to attack the gigantic elephant and of course killing everyone in the process. Jack will use the power of Kaido's ships to attack the elephant and to take it down. The fierce battle could be prelude to what fans have been waiting for: everyone vs. Kaido.

'The Nightmare Returns - The Invincible Jack's Fierce Attack' is 'One Piece' episode 773. Episode 774 is 'A Battle to Defend Zou - Luffy and Zunisha' and will air on January 29, 2017. 'One Piece' streams via Crunchyroll and Funimation.com.