Captain Sharkrider is one of the characters of the pirate crew that Isidro and Mule are forced to fight to save Schierke and Sonia.
When Mule and Isidro show up to save the day, Sharkrider himself challenges the duo, denouncing the name of "pirate" and claiming to be a reformed ship captain under the orders of the government. However, after quickly dispatching Mule, whose academic fencing style is no match for the unsteady terrain offered by ships and docks, he's impressed by the rougher, Guts-influenced style of Isidro, enough to offer the young boy a position as one of his crew. Upon Isidro's refusal, he tries to kill Isidro with a switch blade concealed in his peg leg, but the attempt fails, and Isidro, Mule, Schierke and Sonia are able to escape during the commotion caused by Azan.
Later on in the series, he attempts to ambush Roderick's naval vessel, while Guts and company are aboard, and fails spectacularly losing two of his ships and taking heavy damage on his own.
After he fails, the ship is engulfed in some sort of evil spirit, and gains the ability to go underwater to attack. As it turns out, the pirates made friends with a sea monster which attack Roderick's ship. It also appears as if the "mist" that swept across the earth, transformed Sharkrider and his crew into somewhat semi-apostle beings.
Sea monster that aids the pirates takes down many men by consuming them but Guts comes and manages to defeat the sea monsters with ease. It seems that the tentacle-like monsters are only limbs for the actual monster resembling an octopus with a huge mouth with lines of teeth. When the sea monster proceeds to eat Guts alive, Guts uses both his cannon and the recoil of the shot to swing his sword at the monster, apparently killing it.
Sharkrider keeps on saying that they have more to fight but then Roderick says he has done preparations and orders his ship to fire at the pirate ship. Pirate ship takes damage but not enough to make it sink. Sharkrider curses at them and claims they will be "blown by a coming storm" but one of the pirates shouts that the sun rises. Apparently the sunrise forces the ship to go underwater, meanwhile the pirate captain says they will meet again as the ship vanishes into the sea.
Sharkrider appears yet again on the island were the Sea God rests, bringing his whole ship and crew on land to once again face off against Guts and his party. It is here that he formally introduces himself and explains how tonight's full moon is the festival of the Sea Gods rebirth, we also see that the interior of his ship has a sea slug-like monster that was responsible for the minor tentacles from before. Guts however goes berserk and charges straight for the ships cladding and stabbing the ships monster in the head. Guts then goes on to attack the many other sea slug monsters surrounding him. Sharkrider then disappear, but later appear at the sea god's shrine. There he tells Guts that the sea slugs Guts fought earlier was only one strand of the Sea God's beard.
Sharkrider and his crew attack the Sea Horse and are revealed to have been eaten and assimilated by the Sea God, as they are attached to the slug-like beast inside the ship, and they lose their human forms and become tentacles as the Sea God breaks free from this island.