Location: Water Seven City Area
Petitioner: Franky Family Follower
Reward: Mouse Repellent, 36,000 Berries
Objective Reward: 35,000 Berries

In order to trigger this Side Story you must first make your way through the main story events centering on Water Seven. Once you've infiltrated Enies Lobby and defeated Rob Lucci you'll be sent back to Water Seven, and a bunch of Side Stories will appear on the map. This includes Natural Underground Enemies, which you'll find by heading to Canal Restaurant, in the east of Water Seven City Area and north of Dock One. The petitioner is right near the entry bridge.

A member of the Franky Family, this frightened guy is scared out of his wits by the mass of vicious rodents that have invaded the sewage treatment plant in the Sewer beneath Water Seven. He wants the Straw Hats to get rid of the Berserk Wicked Mouse that is attacking people in the Old Sewer. Sounds easy enough.

There are several ways down into the Sewer at this point in the story, though the quickest route to your destination is via the Franky Family Follower who's guarding a manhole in the Employee Public Bath area, in the northwest of Water Seven City Area. You can jump to the Yoisa Sign in the Abandoned Factory and then head north to find him. Speaking to him will take you right down into the Old Sewer.

Once you're in the Old Sewer, head south until you reach a pit with several enemies at the bottom. If you look down you'll see several Wicked Mice, including one with a very fancy hat. Grapple down into the pit and approach to engage the lot of them.

Berserk Wicked Mouse

Weakness: Power, Fire

What a group. The Berserk Wicked Mouse and its cronies are all quite a bit more powerful than the average Wicked Mice found in the Sewer, and can take much more of a beating to boot. They all like to hurl bombs, and can hit characters in their area or beyond. The fight still isn't a big deal, and you should deploy your Power fighters to deal with the Wicked Mice. Sanji is especially useful in this battle with his Fire-based Skills, and Usopp and Franky can provide decent backup as well.

Once the battle is over Chopper will determine that the mice were... hungry. Simple enough. Return to the Franky Family Follower in Canal Restaurant to learn a little more about his personal hygiene, and bring the Side Story to an end.