Tohl Narita: “A man got in standing on knees. I made it a design that made it hard to tell whether it was a seijin (star human=alien) or a seiju (star beast, star bem).”
While Narita doesn’t refer to it, the alien’s face should apparently have come from that of a longhorn beetle, and it is found that the costume ended up having rising parts seemingly consisting of nuts and circular metal parts the design didn’t have over its head.
As Narita puts it, a costume the actor gets in standing on his knees was used for Alien Iyros while such a costume had never been seen in the series including “Ultra Q” and “Ultrman.”
Encompassing the use of puppet aliens in “Ultraseven” along with the two-manned kaujus, Dodongo and Pester, in “Ultraman,” it is realized that they always devised to apply a variety of methods to the creation of new kaijus as much free as possible from constraints the style of costumes could inevitably put on characters.
Nevertheless, acting on his knees should have been tough for the actor, Teruo Aragaki, as it could have done a number on the knees while acting, and it would be undeniable that the shape of the kaiju might have made the action less exciting with the constraints unavoidably inflicted on movement.
The form with an actor inside standing on the knees was also applied to Giradorus later in the series.
A recent book on “Ultraseven” told me that the preparatory script of this episode originally put the alien as Alien Sirius and the kaiju Aeschylus, the name from an ancient Greek tragedian while the alien was set to make only his voice audible through an electric brain installed in the spacecraft without his appearance unveiled.
It seems that the kaiju Aeschylus was set to appear with three liquids, red; blue; yellow, that came out of the spacecraft merging to embody the kaiju, and this description on the book makes it more convincing that the character known as Alien Iyros showed up from the capsule that came out of the spacecraft leaving it uncertain whether it was the alien or the kaiju manipulated by him.