While in school one day, Tsubasa Sendou, a young boy whose mother disappeared when he was very young, faints in class. His stepbrother, Tokimaru Sendou, picks him up at the infirmary and drives him home in his motorcycle. While driving home, though, the streets suddenly begin to shift and fill with many coloured, flying fishes. Tokimaru is at his wit's end, a situation made worse by the fact that Tsubasa actually talks to the fish, telling them to leave because Tokimaru is there. Uncomprehending, shocked, and frightened out of his skull, Tokimaru crashes his motorcycle.

The next day, at school, Tsubasa's classmates tell Tokimaru that his brother hasn't been in school that day. Fearing the worst, and aware that Tsubasa has a strange fascination for the sea, he rides his motorcycle to the beach. Just as he feared, he finds Tsubasa there. Tsubasa received a message through his computer on the night of Tokimaru's accident, an encrypted message taunting him with the whereabouts of his lost mother. Now, he stands at the centre of a bright beam of light, the strange, multicoloured fishes re-appearing around him. Tokimaru doesn't understand what's going on, but he knows one thing: he's not letting Tsubasa go anywhere --not without him. Abandoning his motorcycle, he leaps at the beam of light as it closes around Tsubasa, reaching for his brother's hand.
 
 

When the boys come to, they are lying on a strange beach. They've hardly had ample time to wonder where in blazes they are, though, when they are attacked. They manage to escape --by means of a humongous, flying stingray, no less --but only find themselves in the midstt of a raid, huts burning and villagers massacred before their eyes. One of the men attacking the villagers turns on Tokimaru, wounding him across the chest. Tokimaru is no match for the man, but at that moment Captain Shroud, a handsome, blond pirate, makes his entrance. He orders his parrot, Anne Bonney, to take a sword to Tokimaru, the cutlass which gives the manga its title. Tokimaru kills his attacker, not intending to do so. His action takes him by surprise and leaves him stunned. He barely pays attention as Shroud tells him to keep the cutlass, and remains in a disbelieving slump till his brother sits beside him and tells him: "Don't cry, idiot."

Later, after the brothers have managed to build a fire, Tokimaru discovers that Sendou has a fever. He goes in search of any remedy --although we have to wonder what he thought he'd find in a strange, alien jungle setting --he might find, but instead winds up ttangled in the ooze of a large, slimy plant. He is rescued by Ledania, a coquettish young woman who takes Tokimaru to her house and tends to Tsubasa's fever. Ledania, though, appears to be in league with the men who attacked the village. She allows the men to kidnap Tsubasa, giving Tokimaru a poison she hopes will slow him down by means of a kiss. The poison has little effect on Tokimaru, though, who rushes off to rescue his brother.