The Arbalessia Fortress arc follows the Millenium Blue arc. The Straw Hat Pirates enter the deeper parts of the Millenium Blue, known as Sand Sea, which is known for its thick, mudlike water one can even walk on (this is found out by Luffy, who for accident, falls out of the ship) Suddenly, a dagger hits the ground right beside Usopps feet. the crew is shocked and anyone gets ready for action. A group of four marine soldiers, wearing knights armour, assault their ship. Franky and Brook defeat the enemys with a combination attack, which includes Franky shooting Brook into the air and the skeleton man performing some ranged rapier attacks to knock the strange attackers into the sky. Shortly after, they reach the great Mangrove Wood, which consumes most of the center parts of Millenium Blue. There, they meet a group of strongly injured Odyssey Pirates, lead by Marchosias. Altough Zoro advises him not to do, Chopper decides to heal their wounds. The Pirates then tell the Straw Hats that, after Kizaru captured them and the captives were being transported to the Great Fortress Arbalessia, the transport ship was ambushed by Jiguro and his fellow Parable Pirates. In the upcoming melee, they were able to escape, but their captains were still imprisoned by Kizaru. After the survivors get away, the Straw Hats decide to enter Arbalessia, which is said to be on the only island in the Millenium Blue, to get the key they need and to rescue the pirates that sacrificed themselfes for them. The survivors are seen afterwards getting into a fight with a member of the Special Deletion Unit.