Tohl Narita: “While it is similar to the idea about Gavora, an attempt was made to make it look different by covering it with something, which was the shells on the back.”
It is said that the Kemlar costume was planned to be remodeled from that of Gamakugira initially, but, as Ryosaku Takayama found it would require a lot more work to remodel the costume, it was newly sculpted eventually.
Although the design by Narita shows the shells were to cover its head too like Gavora, it seems that Takayama adjusted it so as to make the shells cover only the kaiju’s back.
While, from the design, it appears that the jaw was planned to divide into two and that the costume was sculpted accordingly, the mechanism was left unused although you can see a slit in the center of the jaw where the two parts were supposed to come apart and meet.
It is likely that Kemlar’s weak point was set to be an luminescent organ inside the mouth in the script first and that it was changed to the equivalent on the back.
The light Kemlar gave out when breathing out the toxic gas was to come from the luminescent organ in the mouth. Thus, because the sequence was dropped in which the light from the mouth made Hoshino aware of the luminescent organ in the mouth as its weak point, it ended up making Hoshino’s remark sound unnatural in the completed film as he abruptly specified the luminescent part on the back as the kaiju’s weak point.
The change seems to have been made as the weak point on the back would make the fight scene look more picturesque than the one in the mouth. The luminescent organ was made by Shigeo Kurakata using a rubber ice pack and an air pump to inflate and deflate it.
In the script, chances are that Kemlar was supposed to unfold its tail like a peacock without any depiction of the shells on the back unfolding.
Takayama wrapped vinyl leather he bought around its tail saying in his diary it looked so impressive when the whole tail was wrapped with the material as it made the tail look like that of an earwig.
Tetso Yamamura says in a book that the shells were made from FRP and that they were excellently sculpted while I find it very much attractive that the shells look so different between the front side and back side.
Incidentally, as the word for smoke is “kemuri” in Japanese, Kemlar is named after that while Kemur was named as such because it vanishes like kemuri.