Spoiler alert: The following section contains plot-specific details.(Skip Section)
The episode starts with Tiff collecting shells on the beach. Soon, she finds a golden shell with a love note from Kine. She finds Kine and tells him that it is not possible for them to be together due to the differences in their environments and refuses. King Dedede watches all this and offers to make a deal that if Kine reveals his home's location, he would make it so Kine could live on land. However, Kine does not know that Dedede wants to build a resort in his home, and tells Dedede where it is. Dedede partly keeps his promise, by putting Kine in a large aquarium on wheels. But Kine finds out life on land is rough, almost being sliced in half by Chef Kawasaki, nearly eaten by Dyna Blade, and falling from the sky into the mayor's house. Eventually, they find out what Dedede's true intentions are with Kine's home. Kirby stops him with Tornado Kirby, and the marine environment is saved. Dedede and Escargoon are chased away by Joe the Shark, and Kine finds new hope when Kirby is swimming with a snorkel. The episode ends with Tiff calling to Kirby that he's in big trouble for giving Kine the idea.
End of spoilers
Changes in the Dub
The beginning scene seen from Kine's point of view was shortened in the English dub most likely due to time constraints.
When King Dedede and Escargoon realize that they've made it to the Rainbow Coral Forest, there are originally several shots of the location before cutting back to the two. In the English version, there's only one shot of the ground before cutting back to the submarine.
After Kine is sent flying when his tank crashes against the tree in the heart of the village, there's a small scene where Chef Kawasaki is asking Dr. Yabui if he wanted to fish. This part was cut out of the English dub.
The scene where Kine first interferes and yells, "Stop!" was cut out of the English dub in favor of a commercial break after Kine's silhouette is revealed.
When Tiff is seen on the shore, she's originally silent, but in the English dub, she's more vocal and even says "wow" when she sees the shell she picks up, whereas Tiff only gasps with delight in the original.
When Tiff opens the shell in the original, the ancient language written inside was originally called Pupupumoji, but in the English dub, they were renamed to "ancient cappy-glyphics"
In the original, the message said that Kine had waited every day and night to see Tiff and finally got the courage to send the message. In the English dub, he only says he saw her recently and wants to meet her that evening.
When Tiff is leaving the castle to see Kine, Tuff is with Kirby; the former asks where his sister is going and she claims to be leaving to collect seashells. Her brother asks why she's going in the evening, but she tells him to leave her alone. Despite this, Tuff concludes that she's not carrying any tools to collect sea shells just before she leaves. In the English dub, Tuff instead asks if Tiff wants to play Hide & Seek, only for her to say she won't be able to because she's just heading "out" just for Tuff to say it was dangerous since the time was evening. Tuff then asks why she's wearing their mother's perfume, only for Tiff to say it wasn't his business before leaving.
In the Japanese version, the reason why King Dedede and Escargoon are trying to build a submarine was to dig up resources. In the English dub, it was changed to a plan about making an underwater castle. The reason for this change is unknown. 
When Tuff and Kirby are hiding behind a rock, Tuff originally feels excited that they might know Tiff's secret and tells Kirby that he has to hide too. In the English dub, he muses over how they seem like secret agents and that Kirby has to play the part by keeping quiet.
When Kine meets Tiff, he greets her by saying, "good evening," but in the dub, he just says he's happy to see her.
Kine admits to being able to somehow write in Pupupumoji, but in the dub, Kine explains that he and other fish are well educated because they're in "schools."
Tiff asks why Kine asked about her interests, only for him to say that she's stolen his heart. In the English dub, when she says she "loves" marine biology, he took it personally as a confession of love to him, and actually confesses that since they have a lot in common, she should be his girlfriend.
When Tuff and Kirby reveal themselves, Tuff is talking to Kine in the original about how pointless it is for him to get her affection. In the English dub, Tuff is instead talking to his sister about how fishy the situation was, but didn't know it was this fishy.
In the Japanese version, Tiff said she'd think about being his girlfriend only if he could get on land and survive somehow, and after she runs away, Tuff calls Kine a dumb fish. In the English version, Tiff instead says that since she can't live in water and he can't live on land, he'll have to forget their relationship and Tuff instead expresses his sympathies by saying she was right and that it was too bad he didn't have lungs.
The Rainbow Coral Forest was renamed to the Rainbow Coral Reef.
In the library when Tuff confronts Tiff, the latter says that she has some feelings for him since both them and fish are types of vertebrates and most likely even evolved from fish. She then says that she might be his girlfriend since the two of them aren't so different, but in the English dub, she starts to have feelings for him since he's polite and able to write so well, but denies being his girlfriend, even denying the chances of a date unlike the original version.
In the Japanese version, Tuff told Kirby to get Fololo and Falala, but in the English dub, he instead suggests that he and Kirby can help wheel Kine around Cappy Town.
When Kine is flopping about Chef Kawasaki's kitchen, the latter repeatedly says "hold it!" while Kine repeatedly shouts "No, no, no...." In the English dub, Kine is silent in this pursuit while Chef Kawasaki just tells him to cease his struggling and get on the chopping block.
As King Dedede is destroying the Rainbow Coral Reef, he's singing about how the sea is his. In the English dub, he takes comfort in knowing that he'd have the land cleared quickly.
All profanity was removed from the English dub.
In the Japanese version, when Kirby confronts Dedede, the latter swears and becomes angry that he shows up at a key moment, but Escargoon is quick to reassure him that Kirby might've been unable to inhale underwater. In the English dub, Dedede just questions why Kirby was present and Escargoon makes a rather obvious conclusion that Kirby must've been there to stop them.