Chapter 891 is titled "Believing in Me".
The Stories of the Self-Proclaimed Straw Hat Grand Fleet Vol. 23: Leo Arc - "Boys! We're gonna rebuild every last building in town!"
While Charlotte Flampe has her subordinates try to attack Luffy, he continues to be overpowered by Katakuri, but keeps getting up and fighting back, trying to strengthen his Kenbunshoku Haki. On Whole Cake Island, Stussy mentions to Niwatori and Mont-d'Or that the Tamatebako was what caused the collapse of the Chateau, and out on the sea, Sanji's team finally completes the cake right as Big Mom threatens the Thousand Sunny with a gigantic Prometheus.
In Hakuriki Town on Komugi Island, the citizens were shocked by mirrors breaking due to the battle between Katakuri and Luffy in the Mirro-World. They comment their surprise on how long this fight has gone. On Whole Cake Island, Count Niwatori also remarks on this after seeing that it is already 9:30 PM. Next to him is a table where Stussy and Morgans sit, and Stussy reveals to Niwatori and Mont-d'Or that the Tamatebako given to them by the Straw Hats and Fishman Island was the cause of the explosion that toppled the Whole Cake Chateau.
In the Mirro-World, the 36th daughter of the Charlotte Family and leader of the Katakuri Fan Club, Charlotte Flampe, orders her subordinates to assist her older brother Katakuri by sniping at Luffy. However, Luffy is too fast and the snipers keep missing, causing her to stab one of them with a fork. She reveals that since Katakuri is the favorite of all his younger brothers and sisters, she needs to work to gain his favor so she can be the favorite of all her 41 older brothers. She also does not want Katakuri to have this much trouble taking down Luffy, who is still very persistent even at a disadvantage. Luffy gets up from the floor, but Katakuri quickly creates more mochi donuts and assaults him again with mochi arms. Luffy unsuccessfully attempts to dodge, but the Sweet Commander hits him with a mochi kick and sends him crashing into the wall while smothering him with mochi. However, Luffy breaks out through the other side of the wall, and Katakuri states that falling down is itself shameful. Predicting Luffy's actions perfectly, Katakuri hits him in the head and then the shoulders to prevent him from getting up and attacking. Luffy does manage to regain his calm and counter Katakuri's giant punch, and though he is overpowered again, Katakuri notes that he is managing to see into the future infrequently. The Sweet Commander tells Luffy to give up, saying that Big Mom's fleet will take out the Straw Hats before they can make it to Cacao Island, and will be lying in wait for Luffy should he make it out of the Mirro-World. However, Luffy disregards Katakuri's statement and promises to make it out of the Mirro-World.
On the Nostra Castello, Sanji's team completes the wedding cake, and everyone onboard celebrates. Sanji thanks Pudding and Chiffon for helping him, and Pudding has a mood swing, threatening that the Big Mom Pirates may have already destroyed the Straw Hats and Big Mom may not even like the cake. As Chiffon scolds her, she then reverts back to her nice personality and gasping in shock at her words. Both Sanji and Luffy then say that they will head back to their crew because the others are believing in them.
At sea, Chopper activates Monster Point, amazing Perospero. With Prometheus increasing tremendously in size and the ocean water not enough to stop it, Chopper prepares a last-ditch effort to grab Big Mom and drag her into the ocean with him. However, Nami sees the Nostra Castello in the distance, and Big Mom catches the scent of the cake's aroma.
- Stussy reveals to the Big Mom Pirates that the Tamatebako was the cause of the explosion that led to the Whole Cake Chateau's collapse.
- Charlotte Flampe, the 36th daughter of the Charlotte Family, is introduced.
- In the initial printing of her debut chapter, Flampe was introduced as the 33rd daughter of the Charlotte Family, making her older than Charlotte Pudding at 15 years old. This was corrected on the day of the chapter's release.
- The cake is finally finished.
- Luffy is beginning to see into the future like Katakuri.
- Big Mom smells the cake.