Disclaimer: The following post and the core idea behind it are solely one of my theories about a peculiar in-game model, but none of it is canon.
Now for the actual theory, let's visit the Hateno Tech Lab.
There is a lot of various Sheikah-type debris lying around; screws. plates, propeller blades from Skywatchers, etc. ...and hanging from the ceiling, this thing right here.
It does not look like it is a part of any existing Guardian - rather, it looks like something unique and already assembled. But what is it?
I think that it might be the in-game model of a fifth, scrapped Divine Beast. And there are frankly quite a few points why it makes sense. For example, the Creating a Champion artbook has concept art from when the designs of the Divine Beasts weren't yet finalized, and would you look at that? There is a manta ray (lower left corner)[^1]
The body of the in-game model is a little more plump and with whale-like flippers, but it has the same "tusks"/lobes than the manta from the artbook, and the core concept of a swimming Divine Beast would have been the same either way. It might even be a hybrid as the in-game model lacks a fluke and instead has a long-ish, pointy tail.
... and let's be honest here, the other Divine Beasts aren't exactly anatomically correct either. I'd chalk that up to artistic freedom.
Butt hat isn't all. No matter where you are in Hyrule, you can walk a dozen steps into any one direction and you WILL find something you can interact with: Koroks, NPCs, signposts, trees, mushrooms, enemies, animals, loot, chests, barrels, crates, rusty weapons, memory locations, blupees, buried chests, breakable rocks etc. etc.
...and then there is this giant bay here which has nothing of interest to offer besides a single boring island in the middle. It even has a name, but is otherwise completely irrelevant.
That bay is bigger than the entire Great Plateau, yet it has less content than the dang Woodcutter's Hut. And what little content this bay DOES have to offer, is simply boring. The most interesting item here is a chest with ten arrows. That feels like a joke, but not a particularily funny one.
Why does this giant waste of space even exist?
Well, there ARE similar places like these, mostly devoid of content - like for example the almost barren plain in Central Hyrule where the last bossfight takes place, the area around the crater of Death Mountain where Rudania stomps around, or the part of the desert where Naboris happily zaps passerbys. Giant creatures need a lot of space.
Now an XXL mecha animal stomping in a circle wouldn't exactly fit into Link's backyard, but it WOULD fit into that empty bay perfectly, making its rounds around the only island smack in the middle of it much in the same manner as Medoh circles Rito Village. With a water-bound fifth Divine Beast, that area would have an actual purpose and wouldn't feel nearly as pointless.
...but in order to make such a Divine Beast work, you need underwater exploration. The lack of underwater content has been one of the no.1 complaints about the game since release, and I can't help but feel like it WAS planned but got scrapped some time during development.
Why? Because there IS underwater content. Lots of it, even. An in-game example that you can easily recreate yourself is in Lurelin: From above, even during bright sunshine, the mini bay here doesn't look much different from any other body of water. It is blue, it has waves, end of story. Nothing to see here, move along.
That all changes when the Fire Nation atta- ehrm ... when you shove Link under the dock and wiggle the camera around a bit until you get an underwater view of the mini bay.
Beautiful reef, isn't it? Brightly colored anemones, swarms of tiny fishes, seaweed, sponges, corals, mussels ... all highly detailed, but the only thing you can see from the surface are dull, grey blobs. Someone spent a lot of time and effort creating a vibrant, fascinating environment - but why put so much energy into something that the player was never supposed to see in the first place? It doesn't make sense.
Unless, of course, the player WAS originally meant to see it up close.
Other, older Zelda games, like for example Majora's Mask or Twilight Princess, already had underwater content, so it isn't as if the devs had to invent balanced underwater controls from scratch. And for all of these games you always needed a special item to "unlock" the ability to dive and swim underwater first ... and guess what? Breath of the Wild has a perfect candidate for that: The Zora Armor.
It has 3 parts, and each one offers one level of swim speed up. The chestpiece grants you the ability to swim up waterfalls - somthing you can noch achieve with elixirs, food or other armor pieces. The helmet grants you the ability to execute a spin attack while swimming, which is also unique and can not be achieved by any other means. And the Zora Greaves ... complete the set. That's it. They don't do anything out of the ordinary.
ALL other armor sets in Breath of the Wild have their effects distributed evenly: Either all 3 items have an effect, or none has. The Zora set is the only one where two out of three pieces do something special and the third merely exists for the sake of existing.
What if the greaves were originally meant to grant the player the ability to walk underwater, in a toggleable manner like the Zora Mask from Majora's Mask? The N64 controller has noticably less buttons than the switch, and they still figured out an easy way to change smoothly between swimming and underwater walk. It would have been an effortless no-brainer to just recycle the same mechanic.
Some of the "impossible" chests would also make sense then: there is at least one chest in that bay that is stuck in the ground, but you can not get close enough to it to reach it with magnesis ... something that wouldn't be an issue if the player were able to dive down, stand next to it and use magnesis underwater to shake it free.
Oh and you GET the greaves in the Zora's Domain "city" ... which also has lots and lots of water around it, with zero content except for the occasional duck. The only things you can do down there are:
It would have been a neat, enemy-free tutorial area to get the hang of the underwater controls, maybe with a little race/minigame. As of now, the sunken part of the city feels like a blank spot on an otherwise brigthly painted canvas. There is something missing here, and once you notice it, it is hard to ignore.
And then there is Lurelin village. An entire village, with an unique art style, 'Hylians' that look like they are actually their own unique tribe (similar to Gerudo), their own music, their own culture... they have all the same "benefits" the other towns offer, like an inn, a general store, their very own elder, a uniquely decorated Goddess statue ...
What the village does NOT have, is a purpose. They just exist, but are cut off from the main story. ALL other settlements have some sort of connection to the overarching story or contribute major gameplay elements: Rito Village, Zora's Domain, Goron City and Gerudo Town have their own Divine Beasts and Champions, and in case you missed any ofthose villages, the unique quest to build a village in Akkala will send you to each one. Hateno has the Tech Lab where you get the Camera Rune and Hyrule Compendium, which in turn unlock more quests. Kakariko is the home of Impa, who gives you a main quest (memories) and adds lore to the story. Korok Forest is a "village" you will visit if you want to get the Master Sword, which is THE most important item in Hyrule.
Yet you can ignore Lurelin entirely and the overarching story won't change. It feels almost unfair that this charming village is so irrelevant.
Another detail I noticed, tho this might tiptoe into nitpick territory, is that the map layout would have been a lot more aesthetically pleasing.
If you divide the map into four equal parts, then you have Hyrule Castle and the Calamity Ganon fight in the center, Medoh in the northwest corner, Naboris in the southwest corner, Rudania in the northeast corner, and Ruta ... in a weird place straight east, with the southeast corner being unoccupied. But if there was originally going to be a Divine Beast there, it would have made sense to shove Ruta out of the way and into that odd spot to make space.
Another odd detail are the Blights.
Thunderblight uses lightning. Fireblight uses fire. Windblight uses wind. Waterblight ... uses ice. The arena is filled with water, but the Blight itself does not have a single actual water-based attack.
When Waterblight floods the area, I'm always reminded of the Water Temple boss from Ocarina of Time: the room has the SAME layout with 4 rectangle pillars protruding from the water. I fully expected the water itself to attack ...or at least do something interesting.
Now you may argue that ice is nothing but frozen water anyway, and you're right. But the rest of Zoras Domain and the Ruta dungeon itself revolve around water ONLY. There is no frost involved whatsoever.
What if Waterblight was originally meant to be Iceblight? Look at Zora's Domain: slippery half-translucent, "ice"-looking rock formations everywhere, and that Zora don't do well in too cold environments is something we already know from Ocarina of Time and Twilight Princess.
I wouldn't be surprised if the original idea was to have Zoras Domain frozen over, and they decided against the idea last minute as to not recycle old ideas from former games and/or because there are already too many cold zones on the map. It would have made a bit more sense than fish people being concerned about having too much water.
Seriously, King Dorephan's explanation feels like an afterthought. He claims that the reservoir might burst and "Hylian lives downstream will be in danger", but there is literally not a single Hylian settlement downstream - only monster camps, from the (headspring) to the (wetlands).
The actual Waterblight and its Divine Beast would then have been free to appear in Lurelin, creating harsh currents that made it impossible to travel by boat or catch fish, which IS a pretty big problem for a village full of fishermen and traders, and Link beating Waterblight 2.0 and "Vah Manta" would restore the ocean and thus Lurelin's everyday life to normal.
Having FIVE Divine Beasts would also have avoided a Japanese superstition:
The Japanese word for "four" 四and the word for"death" 死 are both pronounced shi. It is said to bring bad luck to, for example, give someone a gift containing 4 pieces of anything, because it bascially means that you wish death upon them^2. This superstition goes so far that some buildings, especially hotels and hospitals, don't have a fourth floor, or parking lots skip the fourth parking space because noone would use it anyway.
And this has even affected videogames.
For example, Crash Bandicoot. It was created by an American studio, and since that superstition isn't known in America, they didn't have any reason to avoid the number four. Crash Bandicoot has four fingers on each hand, and noone cared about that fact.
...until the game became popular enough to tap into the Japanese market. Suddenly there were concerns about it, so the studio gave that character additional fingers especially for the Japanese release.^3
By the way, NONE of the tribes in Hyrule have four fingers or toes. Hylians, Gerudo and Sheikah have five of both, Rito have 3 toes and technically 5 "fingers", Zora have 5 fingers and two toes, and even the enemies follow that rule, with Bokoblins having two toes and three fingers.
It is a tiny bit weird that they avoided having the number "four" appear in their game on such a minuscule, nitpicky level, but then they're completely fine with four Divine Beasts, four Blights and four Champions. On that huge scale, it suddenly doesn't matter? Odd.
Unless there have been five and one got scrapped.
I admit that last part is a bit of a stretch, but all in all, there are just too many coincidences that fit right into such a theory.
Thanks for reading =)
[^1]: Creating a Champion artbook, page 206
