[1] The film is about a group of Japanese reporters who discover an infant monster called a Gappa on Obelisk Island.

[5] An expedition from Tokyo heads to Obelisk Island, which the greedy Mr. Funazu, owner of Playmate Magazine, wants to turn into a resort.

They enter a cavern blocked by a fallen statue and find a giant egg, out of which hatches a baby "bird-lizard" monster, referred to as "Gappa".

Inside the caverns, Gappa's two parents rise from the subterranean waters beneath the volcano, destroying everything in their path.

Hiroshi, Itoko, Saki, and expedition scientist Professor Tonooka try to persuade the headstrong Mr. Funazu to let the baby go and return it to its parents.

This concept got the furthest into development out of the four scrapped projects, receiving a plot synopsis, speculative screenplay, and kaiju ideas.

Principal photography on Gappa lasted for about 40 days, twice the time that director Haruyasu Noguchi usually took to shoot a film.

In contemporary reviews, Variety stated that the creature Gappa makes an "auspicious debut and reveals itself as "best monster" so far".

[16] The review complimented the film, noting that "the effects are excellent and the script is worthy of a witty children's comedy.

"[6] Galbraith commented on Akira Watanabe's effects, opining that they were "okay but lack the perfectionist drive of Eiji Tsuburaya's work.