Previous story
During their experiences on Dress Rosa and Green Bit, the Straw Hat Pirates was separated from each other and split into two groups after Big Mom suddenly appeared with her pirate gang, requiring action on two fronts. Because of this, Sanji, Nami, Chopper, Brook, and Momonosuke, as well as Caesar Clown, who had been taken hostage, were already sailing ahead on the Thousand Sunny towards Zou Island, where they planned to meet up with their nakama again later. It wasn’t until after Luffy’s victory over Donquixote Doflamingo that the Straw Hats were finally seen again, after docking at an unnamed island. As it turned out, however, only Sanji, Chopper, and Crown were still on board, as the other three had been forced to flee into a dense forest, where they were in turn pursued by a man named Sheepshead and his men.
The fight

Sheepshead, on the other hand, was a subordinate of Emperor Kaidou himself, and seemed to be searching for the samurai Momonosuke. While Nami and Brook ran off with the boy in tow, the earth suddenly shook until a mountain seemed to spew out vast amounts of water. This put Brook and Momo in particular in danger, as they were devil power users who couldn’t swim, so it was ultimately up to Nami to rescue her two companions from the floodwaters. Sheepshead in turn took advantage of this situation to attack. Having eaten from an unknown Devil Fruit, he was able to transform his hands into sheep horns and then attacked Nami with his “Sheeps Horn” technique. Brook, who had regained his strength, countered this with “Soul Ballad”, just as Sanji appeared on the scene and intervened in the fight as well. After a well-aimed hit of his “Mouton Shot” Sheepshead went down defeated. His followers were so shocked that they retreated for the time being.