Inverted with normal-sized Fujimoto and HUGE Granmammare. She can shrink herself to almost-human size, but she's still head and shoulders taller than Lisa.
Played straight with Ponyo and Sosuke at first.
Humans Are Bastards: Subverted and deconstructed. Fujimoto is resentful towards humans for polluting the sea, yet when Ponyo falls in love with Sosuke he is forced to rethink. By the end he sees how, despite doing some messed up stuff as a whole, humans individually can be nice guys. Probably not incidentally, Ponyo's first encounter with humans is a trawling ship cleaning up junk and sludge from the ocean.
Its a Miyazaki film, if you've seen the previous works you'll know this is a given. It just a more low key version this time.
Kick the Dog: Fujimoto mentions offhandedly that he plans to eradicate human civilization by using magic to create a new era of sea life. This is quickly derailed by Ponyo in her eagerness to return to the surface. As a result, prehistoric fish appear (specifically Devonian, even though he mentions the Cambrian Explosion) but humanity goes on.
Licked by the Dog: If the personification of the sea and all sea life liked you enough to marry you, you're probably not that bad a person. They have a LOT of kids too. Ponyo's got to have at least fifty sisters!
Lighter and Softer: In America, fans were rather... surprised at how kid-friendly Ponyo is compared to the generally more all-ages/adult-skewing Studio Ghibli output.
Mobile Fishbowl: Fujimoto is forced to take a back-mounted machine with him whenever he ventures onto dry land, as it carries a vat of salt water that he must spray around himself to keep himself humidified. Still, he is biologically human, which requires him to wear a bubble underwater.
No Endor Holocaust: Although Ponyo raised the water level high enough to drown almost all of Tomonoura, no harm seems to have been done to the town, its inhabitants, or any of the fishing ships nearby. The explanations are three-fold: 1. It's a kids' movie. 2. They're probably prepared for flooding, considering they live on an island. 3. The goddess of the sea was in an extremely nice mood that day.
No Social Skills: Ponyo doesn't "get" humans, and thus makes a lot of gaffes — like carrying a bucket and towel to the table, referring to sandwiches as "milk" as the result of a conversation with a breastfeeding mother, and others. She also doesn't understand that when water comes from people's eyes, that means they're sad.
Only Known by Their Nickname: Ponyo's real name is Brunhilde. "Ponyo" is just the name Sosuke gives her. Her father doesn't exactly roll with it, but her mother likes it.
Reality Subtext: Miyazaki made Ponyo as a means of trying to reconcile with his estranged son (the one who directed Tales from Earthsea). Throughout the film Sosuke and his father are separated.
Reality Warper: Ponyo (as implied by her dad), since she can cause a tsunami, wipe out at least one whole town, gather up every ship in the sea, and bring the moon a couple thousand miles closer to earth with no ill effects. It's not quite clear whether that was her doing or a result of the magic from that well-thing that she accidentally set loose.
Red-Headed Hero: The titular character of course... although the shade is more of orange than red.
Reset Button: The town looks as splendid as ever, considering it has been fully submerged by the ocean. Then again, the goddess of the sea was involved.
Ponyo has three "stages" of transformation: fish, Mr Toad frog/amphibian thing, and human. When put in context with Fujimoto's talk of evolution and pre-history, Ponyo's speed evolution is a nice touch.
Ponyo's sisters breaking her out of her bubble look extremely similar to sperm cells having at an egg.
It's not surprising that the movie is crowded with little girls, young mothers and elderly obaa-san, because they're all women at different stages of the life Ponyo desires.
There's a Totoro magnet on the refrigerator in Sosuke's house, Lisa briefly sings a line from the opening song of the same movie ("I'm happy as can be!"), and Ponyo flashes Totoro's signature smile the first time she grows teeth.
When Sosuke and Ponyo traverse the flooded town, they come across a tunnel remarkably similar to the one in Spirited Away.
The little girl, Kumiko, who Ponyo drenches with water, resembles a young Kiki.
Somewhat unexpectedly, the movie also references The Ring of the Nibelung. Ponyo's original name is Brunhilde, and like the character of the same name from the opera, she's a supernatural being who defies her father and falls in love with a human. In case someone thought all this is coincidental, the connection is further emphasized when "Ride of the Valkyries" plays during the climactic tsunami scene.
True Love's Kiss: But it's not the big deal that it usually is, probably since the protagonists are young children around the age of five.
Tsundere: Lisa is an interesting adult version of one. Just ask her husband.
Unusually Uninteresting Sight: Ponyo is a fish with a face, but nobody finds that strange (save one elderly woman who is treated as being a tad paranoid anyway). There's also Ponyo's "chicken/frog legs" when she uses magic, Sosuke's giant toy boat, the underwater jellyfish dome that covers the senior home... The people of this town seem to be pretty chill.
Sosuke: (After seeing a wave with eyes.) That was weird.
Well-Intentioned Extremist: Fujimoto appears very similar to Jung Zorndyke of Blue Submarine No. 6. In the beginning. He quickly becomes a Harmless Villain because Ponyo accidentally foils his plans to cover the world with a prehistoric ocean and at the end he is only genuinely worried for his daughter and for the planet.
"Where Are They Now?" Epilogue: Exceedingly brief: one shot during the credits shows Ponyo happily playing with the other kids at Sosuke's kindergarten and Fujimoto talking to humans on the surface.
What Happened to the Mouse?: Ponyo, while still possessed of her potion-boosted fair-folk sea powers blesses an infant child. While her parents help clean up the damage she caused at the end of the movie they never actually reverse it, and the child is never mentioned again. So there is a random kid in town with the blessings of a sea-goddess. Take that Aquaman!
Wise Beyond Their Years: Sosuke, sometimes Up to Eleven. Beyond the heroic scenes he gets, it's impressive how he mans the signal light - he reads, writes and mediates between his parents who just had a fight because his father had to stay out at sea.
He also knows an astounding amount about extinct sea life. He even recognizes that all of the fish he sees are from the Devonian. Possibly justified, as prehistoric fish are to the Japanese what dinosaurs are to large areas of the Western world, so a 7 year old could very well know a lot about those fish.