For the longest time now, some anonymous user(s) have taken to putting the Kaiju category on Choju pages, and they maybe wonder why those edits are undone, and the pages protected. Well I suppose it's long past time I explained.
Now to be frank, no one is really sure what the definitive difference is between Choju and Kaiju is. However, there are several instances in the series itself, that implies there is a major and important difference.
All Choju were created by Yapool, either literally or mutated by him from some prior being, sentient or otherwise. Monsters on the other hand, appear to be mostly mutations, or life forms that evolved in environments atypical to what you would find on Earth.
It was stated in Ace (and later made irrelevant in Taro.....) that Choju are stronger than Kaiju and stated again in Mebius. Also note, that in Mebius an effort was made, in and out of universe, to differentiate between the two.
While Kaiju are organic, even the ones controlled by aliens, Choju have been described as 'kaiju weapons' or similar descriptions. This, mixed with some of their behavior, gives the impression that they are not organic. Even the Choju that were once normal beings, aliens or kaiju, seem to be something akin to cyborgs, than simple mutations. Yapool has even taken control of them before and given his nature, it is presented as data being uploaded into a network, than simple possession.
Yet...they are clearly not robots, which is what I think causes much of the confusion (for some, some people still but Kaiju on pages about robots...) However, I think the issue can be resolved if we think less in metal panels and circuits and more in the direction of biotech.
Now whether I prove Choju are not Kaiju, is a moot point, the policy of this wiki, has been, Choju are not Kaiju. That's what the series presented, that's what we go with. Even if merchandising treats the two groups as the same, the lore of the Ultra Series is that they are different.
That said, it is best to think of Choju not as kaiju, but things similar to mechagodzilla, technology/weapons crafted in the shape of kaiju. The only difference is that instead of simple metal, Yapool may have used organically grown materials. However, the end result is that Choju brains have more in common with robots than the animal minds of Kiaju.