Kikwis were already endangered in Skyward Sword era. The octoroks were an invasive species which had offensive power that the kikwis lacked. As a result Octoroks became a species with large population whereas kikwi populations decreased drastically.
THEORY 1:
Finally, mutants like Bucha started to appear. The normal***s in the population started to call them as elders. As the mutants finally were dominant, they lost their capability to camouflage instead, they had offensive power and humanoid abilities. They started to wield slingshots. But with the evolution of monsters, slingshots proved to be ineffective and were finally wiped off
THEORY 2:
The Kikwis went into dual mode like this jelly fish
The plant Kikwi could be equated to Polyps and the mobile Kikwis could be equated to Jellyfish. Therefore the Great Deku Tree is a Kikwi like Bucha. Over a period of time, the Deku Tree lost the ability to reproduce. While the "Polyp" started getting attacked by herbivores, the "Jellyfish" started getting attacked by carnivores. Deku Tree grew steadily grew finally to the point where it cannot be harmed even by the biggest herbivores.
THEORY 3:
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However this doesn't explain what happened to other Kikwis. But, they must have gone extinct of they remained that way in the presence of superior species, say, Octoroks (offense) or Korok (superior camouflage)
THEORY 1:
Finally, mutants like Bucha started to appear. The normal***s in the population started to call them as elders. As the mutants finally were dominant, they lost their capability to camouflage instead, they had offensive power and humanoid abilities. They started to wield slingshots. But with the evolution of monsters, slingshots proved to be ineffective and were finally wiped off
THEORY 2:
The Kikwis went into dual mode like this jelly fish
The plant Kikwi could be equated to Polyps and the mobile Kikwis could be equated to Jellyfish. Therefore the Great Deku Tree is a Kikwi like Bucha. Over a period of time, the Deku Tree lost the ability to reproduce. While the "Polyp" started getting attacked by herbivores, the "Jellyfish" started getting attacked by carnivores. Deku Tree grew steadily grew finally to the point where it cannot be harmed even by the biggest herbivores.
THEORY 3:
origin of the great deku tree - Zelda Universe Forums
In the forums i have seen people saying that bucha is the great deku tree. But he wasn't very wise. My personal theory is that the great deku tree was the kikwi hermit and that faron mixed with him with the tree. For telling the location of the sacred…
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