this could be some thought provoking masterpiece about the endless cycle of consumerist capitalism. I can't comment on the plot. I don't read Japanese.

I can comment on the combat, which is kind of novel. It's a mix between a standard JRPG, and pool? okay.
Basically both your attacks and your enemies' attacks make you bounce off of the walls, or other characters in the field.
Knocking enemies into your party members allows that party member to attack, and knocking enemies into the walls allows for repeated attacks.
It's kinda neat in theory, but in reality there's only really one kind of arena, and you'll be knocking into your party members frequently, if say, Sanji is in-between Luffy and an enemy. Attack the enemy with Luffy, and he might bump into Sanji, making Sanji bounce away, and stopping Luffy from attacking.
Most of the party members are pretty good so its not that big of a deal, but still annoying.
Another annoying thing is that enemies appear as npc's in the overworld, and you can just redo their fights over and over again, makes actually beating the enemies feel pointless and not very satisfying.

One party member that downright sucks is the protagonist. It's not Luffy, but some random kid that was invented for this game. Sure.
Sadly he also has to be required in your party of 3, meaning you are only limited to having two playable straw hats in battle. Kind of disappointing.

The music and presentation are about what you'd expect from a random handheld that never released in the west.

Unless you are the worlds biggest Wonderswan Color fan, or just plain stupid like me, its not really worth playing more than like 30 minutes of.

Also Sanji is able to attack women??? unplayable.