As Noriyoshi Ikeya himself said, it is not that he entered the field of film art because he wanted to be involved in tokusatsu and kaiju while he was initially called in by Tohl Narita to participate in the production of the series Ultraman.
Therefore the work he did in the field is not confined to kaiju design but he played an active role involved in film art including the films produced by renowned directors and TV commercials after leaving Tsuburaya so that he was awarded the Japan Academy Prize for the Outstanding Achievement in Art Direction twice in the 1990s.
Among the Ikeya monsters, it is fun to learn Takkong that appeared in “The Return of Ultraman” is likely to be thought as a challenge to the Narita design with the quirky shape after Ikeya took over the designing of Ultra kaijus from Narita.
I myself like the design of Twintail as it is admired as a masterpiece created by the combination of Ikeya and Ryosaku Takayama as Takayama modeled the costume along with Gudon and Stegon (the “Siver Kamen” alien costumes were also allegedly made by Takayama while he seemingly modeled the majority of the “Fireman” monster suits as well).
I wish I could have seen more of the monsters worked out by them in “The Return of Ultraman” (by the way, I feel like I wanted to see Zetton II modeled by Takayama again…).
According to an article, Ikeya seems to have said he had in stock design drawings of unreleased new monsters he had drawn every once in a while in his spare time.
I definitely hope these designs will see the light of day in the form of characters shown in film/video products someday.