Mario and Luigi are walking in the Plaza harbor and see the warp to Noki Bay.
Mario: It's been a few hours. I think the bay should be clean now like the elder said.
Luigi: Then let's-a go!
Mario: Hey! That's my line!
They stand in the warp and look at the sun. They appear in Noki Bay.
Mario: What the?
The bay is even more polluted than before. The only water in sight that isn't affected is the water from the waterfall.
Luigi: I thought the bay would be clean by now.
Old Noki: You're right, but I think the pollution is coming in great mass from under the bay. Such great a mass that the waterfall can't get it all. The pollution is spreading out to sea. It'll hit Delfino Plaza if we don't stop the source of the pollution.
Luigi: How do we get there?
Old Noki: I'm afraid you aren't ready yet. You need to train on maneuvering in these wetsuits. Until then, you won't be able to stop the source.
The duo put on the wetsuits (which are only scuba helmets).
Mario: So, where are we going to practice?
Old Noki: In this bottle!
Suddenly, Mario and Luigi are pulled into the bottle by a strange force, shrinking at the same time. Eventually, they stop shrinking and find themselves in the bottle.
Luigi: Sweet!
Mario: Look! A red coin! This is a red coin practice game!
Mario and Luigi split up and go toward the coins. Luigi dives down to the castle on the bottom and finds three red coins on the floor. Mario swims up to the top and finds another 3 coins up there.
Mario: The final two are in that jet stream.
Luigi: I got them!
Luigi jumps in the stream and grabs the final two coins. A Shine Sprite appears on top of the castle. Mario suddenly doubles in size.
Mario: We need to get out of here!
Luigi, who triples in size, tries to swim to the Shine, but is still caught in the current. Mario grabs the Shine Sprite and pops out of the bottle after Luigi. They reappear in Delfino Plaza.
Mario: Well, that was exciting!
Luigi: On to the next Shine!