Location: Water Seven City Area
Petitioner: Iceberg
Reward: Varies; see below
Objective Reward: Varies; see below

In order to trigger this Side Story you first need to finish up with the main story in Water Seven, or at least complete the most important objective: Defeat Rob Lucci. Once the CP9 head goes down you'll unlock a bunch of Side Stories in Water Seven, including the quest sequence Helping Iceberg. To begin the Side Story you'll need to speak to Mayor Iceberg, who is standing outside his mansion in the far north of Water Seven.

Iceberg is either being praised or yelled at by his constituents when the Straw Hats arrive, and he needs help running some errands. Agree to assist him and he'll give you several tasks to complete while he, uh, governs.

Part 1

Iceberg's first task is bringing food for Tyrannosaurus, his pet hamster. Tyrannosaurus likes aqua corn, a crop sold by a man operating a street stall. Jump to the Yoisa Stall on the Water Seven Lower Coast, where the crew first debarked when entering Water Seven, and run towards town. You'll find the merchant as you approach Water Seven... though he was robbed by Pirates, and has no aqua corn.

Continue north until you reach the bridge into Water Seven, then take a right and head south. You'll see three Pirates laughing it up by the shore, near a tree where you may previously have spotted an enormous bicycle. You'll need to take the aqua corn back by force, which is pretty easy since they're quite weak. Take the aqua corn to Iceberg for your reward.

Reward:Aqua Cabbage Roll, 36,000 Berries
Objective Reward: Aqua Cabbage Roll

Part 2

Iceberg is still desperately in need of help, and when you speak to him again he'll ask you to cancel an appointment for him. The receipient of the bad news is the boss of the tableware factory, whom Iceberg says is hanging out near the Employee Public Bath. Head west from Iceberg and you'll find the man outside a big steel door, shortly after entering Employee Public Bath.

In order to get through this conversation you - er, Usopp - must successfully lie to the man. Tell him the following:
  • Iceberg has a press conference
  • He's going to advertise the man's merchandise
  • It's for the city

Next Iceberg needs you to cancel his speech in Fountain Square. Head straight down the stairs to the south of Iceberg and keep running until you find a building. The manager of Fountain Square is here, and he, too, requires a few convincing lies:
  • The mayor has to get ready
  • He's preparing for the Aqua Laguna
  • The mayor trusts you

Last, Iceberg needs you to cancel on the deputy mayor of another town. The deputy mayor plans to meet with Iceberg at a restaurant on the east side of Water Seven, by which Iceberg means the Canal Restaurant to the north of Dock One. You'll find him standing near an entrance with a green facade. Again, more lies:
  • The mayor has a stomach ache
  • There's a dish that is good for stomach aches
  • He said he'd work with your schedule
Return to Iceberg. He'll thank you for your efforts and hand over a reward. You'll also find Iceberg's Record Cube sitting a short walk away from the mayor.

Reward: Elephant Tuna Saute, 46,000 Berries
Objective Reward: Elephant Tuna Saute

Part 3

Speak to Iceberg after completing the first two sections of Helping Iceberg and he'll bring up a third, more troubling issue. It appears that people are being attacked near the Sewer, and he wants the Straw Hats to look into it. Agree and he'll tell you to speak to anyone near the Sewer, in the south of Water Seven.

Travel to the Sewage Treatment Plant and check the entrance to the Sewer. There are three troubled people standing around the stairs to the Sewer, and they'll all mention bats as the culprits. You'll need to enter the Sewer and defeat three Wild Golden Bats. There are Golden Bats in a number of different places throughout the Sewer:
  • In the southern passage of B1F
  • In the western rooms of B1F
  • In the side rooms of B2F
  • In the Old Sewer
You're likely to run into Golden Bats while fighting other enemies, as well, though Wild Golden Bats don't seem to spawn unless you specifically run into Golden Bats while on the map. (That was the case for me, anyway.) 

Return to the man out front of the Sewer once you've defeated three Wild Golden Bats to ease his mind, then speak to Iceberg again to end the quest chain. (Make sure you speak to the guy by the Sewer first, or you'll be making a return trip.)

Reward: Iceberg's Gift, 59,000 Berries
Objective Reward: Rock Bear's Strongarm Soup