Shonen Jump's One Piece (GBA)

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Flags to unlock

To get the flags you first need to beat the game than do the following.

FlagHow to unlock
Alvida pirate flagBeat Alvida in 1-1 then find her in 6-1.
Arlong's pirate flagbeat Arlong a second time around.
Black cat pirate flagBeat kuro the second time around.
Buggy's pirate flagBeat buggy the second time around.
Cook pirate flagget sanji and talk to Chef Zeff in 4-1.
Kreig's armadaBeat Don Kreig the second time around.
Navy flagbeat axe hand morgan or chaser the second time around.
Red hair pirates flagBeat boss battle mode in all difficulties.
Straw hat pirates flagget all the flags but the red hair pirates flag.
Veggie pirate flagit's behind the veggie pirates in 3-1,you have to have Ussop to get past them.

Sound Test

To unlock the sound test in the options menu collect all the mini chests and then talk to gaimon in syrup village 2. (You must have completed the game and have the treasure key before you can pick them up)

Unlockables

Perform the task in order to unlock the thing specified before.

UnlockableHow to unlock
Axe-hand Morgan StatueComplete level 1-3.
Billow-a-bikeComplete level 6-3.
Cat's ClawComplete level 3-3.
ChakramComplete level 3-2.
Chouchou's dogfoodComplete level 2-2.
Elephant TunaOn level 6-1, have Sanji talk to a woman.
Free FoodComplete level 4-2.
Gas MaskComplete level 4-3.
Hatchan's Octopus TrapComplete level 5-2.
LollipopComplete level 4-3.
Mackerel Head OneComplete level 4-1.
Map of the grand lineComplete level 2-3.
Master of the Near SeaComplete level 5-2.
ShigureComplete level 6-2.
Special Buggy BallComplete level 2-3.
Tooth GumComplete level 5-3.
Usopp's Sling shotComplete level 3-3.
WadoComplete level 1-2.
Zolo's Stomach BandComplete level 1-3.