If I had a choice to live in a fantasy world, I would want it to be in an underwater world. Where you would be swimming aside fish and zooming around the globe. Taking the occasional break and heading into zones where there is no water. Laws of physics would be bent, many stunts would be pulled and safety would be prioritize.
There would have to be many ground rules, so that humans don’t chase away the fish, which would become our neighbors and so that larger predatory fish would not eat humans. There would most likely be a new job in each street, that would enforce the law of not killing the fish and each human would be given a taser like weapon that would give a small shock at the designated area. Research would have to be done, so that no fish would be harmed with the shock. Safety for humans and animals would be at the utmost priority.
Another movement that would happen would be taming the animals. A beneficial bond would be created so that fish and other underwater living creatures would help humans. Like a mantis ray helping with transportation. These bonds won’t mean much in the early game, but later down the line, these bonds will become similar bonds to what humans and dogs have. This could leave to mistreatment as well, so another perk of living in the underwater world would be that we all share the same communication language. If the animals knew how to talk, there would be less conflict between us and them. They would also have a voice, meaning they can cry for help or settle things in a very civilized way.

Earth has gone down a very dark path of littering, so in my fantasy world, trash would dissolve rather quickly. Anything that no longer benefits the world, will eventually disappear. Meaning the environment would be extremely clean. This would help us live longer lives and happier lives, now that no one has to do the dirty work. We would also evolve ways that would help us live underwater. Having larger webs (the skin between our fingers) would help us drastically.
Now that we have gills, there would probably be new brands of clothing that protect them from injury and dust. There would also be new clothing that helps us swim as fast as fish in the underwater world. There would also be sports, challenging many people to get faster and faster in swimming. This would test human creativity and possibly create games in which humans and animals team up to beat one another now that animals learned to talk.
There would have to be a significant increase in technology, both quantity and quality. Now that most areas would need light and warmth, a lot of people would not be able to live in harsh conditions. We might adapt and be built for cold and warm environments but since that is not a guarantee, scientists would have to work hard to improve the current electricity system. There would also be laptop like devices that would be better suited for water for the same purpose as current laptops. They would have faster internet because there will be many ways people will create an easier and more efficient way to transmit electricity that would flow faster then the current wifi.

A better version of current cars might be created to transport people large distances, if animals refuse to help with transportation. It would be more efficient and there would be no car crashes because the cars would stop immediately before collision. They might be a few injuries, but there won’t be anything fatal to the human.
There would be a fish king, that monitors the entire world, and prevent conflicts with a blink of it’s eyes. He would be the most powerful creature in the world and would do no bad. He would be brother of Jesus. There would be no accidents, since he would be there to stop it, and he would create many areas where there’s land inside the water. He would spawn animals when they are heading towards extinction. He would create buildings, where the homeless would live and provide food that does not require killing of any animal. Of course, this would lead to many spoiled people in the world, but the fish king does not care about that. He would continue to help them even if the people use him to their advantage. The fish king would be immortal and anyone that would head near it would turn back immediately and forget what they saw. The fish king would live in a pineapple under the sea, he would see the entire world from there. He would present new technologies if the scientist are unable to, this would reduce product prices drastically.

Although there appear that everything has negatives in them, the under water world do not. If one appears, the fish king, would immediately remove it from existence. This would cause anyone to feel joy and live everyday, not needing to worry about many things. The fish king would take care of it. Anyone that feel that they are less productive than some people, and feel bad about it, the fish king would grant them their wish so that no one would need to feel bad in the underwater world. Although the fish king may seem like it’s spoiling the whole world, it has one trait that is keeping the world’s creativity afloat. The fish king is curious. It loves to see what other beings have created, and find joy in them creating something that he hadn’t thought of. He would also favor those who create things that surprise him. You might think that this is unfair but the fish king believes that doing this would keep the creativity on the world afloat and he also believes that, “Nobody is prefect.” Though many people believe he is real and they’re seen real miracles, there are always some that will refuse to believe it. This is not changeable and will probably stay this way.
Photos by Matthew using Canva