As 1/8 humans were humans acted by humans as they were, I have nothing to talk about regarding the design and the making of costumes.
This episode, as I wrote before, was to be produced as one of the “UNBALANCE” episodes in which stories unfold about mysterious phenomena instead of kaijus before the show title changed into “Ultra Q” along with the content shifted to a kaiju series by decision of the TBS producer Takashi Kakoi.
While it was about to be dropped from the series with the shift to a series featuring kaijus, it ended up being produced as Kakoi found normal-sized humans wandering into the 1/8 city could be seen as kaijus (therefore it is likely that the title and style changes were made before this episode was actually produced).
Along with the miniature buildings of the 1/8 city, props such as a telephone and pencil to be used by Yuriko shrunk to 1/8 size were made. The telephone was made of plaster and the pencil tip was from a coke (fuel) piece so that it could allow Yuriko to write letters on paper for real.
Hiroko Sakurai who played Yuriko (and Akiko in “Ultraman”) writes the telephone receiver was so heavy that she accidentally dropped and broke it, and it appears to have a mark on the part where the receiver was repaired (Sakurai says it does).
Without computer-generated images, everything was hand-made back then even with optical compositing used along with the props, which, strangely enough, could give us a sense of presence in its own way apart from how much real they look by today’s standards.
According to one of the books authored by Sakurai, these props were made by an art staff member named Hatakeyama, and she writes she found it so impressive that he was working on the set so happily and vigorously saying he was enjoying his job very much as he could do what he liked to the fullest.
It is explained online that she still has the big pencil used in the show with her.