There are certain franchises that inspired a number of creators in Japan. We see lots of series created in Japan referencing franchises like Godzilla, Kamen Rider, and Ultraman, and Final Fantasy is no exception. The Final Fantasy series has referenced franchises like Star Wars, Star Trek, and even Internet memes, but they also contain plenty of references to Japanese movies and TV shows.
Final Fantasy VII was inspired by a lot of different movies like Blade Runner and Jaws, but some of the monsters in the game are directly inspired by creatures from the Gundam franchise. For those unfamiliar with the series, the Gundam franchise is considered to be one of the seminal works of Japanese mecha fiction, starting with the Mobile Suit Gundam anime in 1979. Since then, there have been a number of different Gundam series and mecha suits from these cartoons inspired the designs for Diamond, Emerald, and Ruby Weapon in Final Fantasy VII.
Diamond Weapon/AMX-004 Qubeley
Diamond Weapon was originally only present in cutscenes in Final Fantasy VII. It walked out of the sea and marched towards Midgar. Rufus Shinra ordered the Mako Cannon from Junon brought to Midgar, so that it could defend the city from the monstrous invader. A blast from the cannon deals with Diamond Weapon, but it fires back and incapacitates Rufus Shinra. The western version of Final Fantasy VII added Diamond Weapon as a boss and it was included in future editions of the Japanese Final Fantasy VII.
Diamond Weapon's design is inspired by the AMX-004 Qubeley suit from Mobile Suit Zeta Gundam. Like Diamond Weapon, the Quebely has massive plated shoulders and similar designs for its armored body and color scheme.
Emerald Weapon/AMX-002 Neue Ziel
Like Diamond Weapon, Emerald Weapon wasn't present in the original Japanese version of Final Fantasy VII but was added for the western release. Emerald Weapon is a superboss that swims through the darkest depths of the ocean, waiting to annihilate any passing submarines that are foolish enough to approach it.
Emerald Weapon's design is based on the AMX-002 Neue Ziel from Mobile Suit Gundam 0083: Stardust Memory. Like Emerald Weapon, the Neue Ziel is a green machine with weapons hidden in its shoulders. Emerald Weapon is an underwater creature, while the Neue Ziel could float through the air and in outer space.
Ruby Weapon/MSM-03C Hygogg
Like Diamond Weapon, Ruby Weapon wasn't present in the original Japanese version of Final Fantasy VII but was added for the western release. Ruby Weapon is a superboss that hides in the sands around the Gold Saucer, waiting for a foolish group of adventurers to try their luck in battle.
Ruby Weapon's design is based on the MSM-03C Hygogg from Mobile Suit Gundam 0080: War in the Pocket. The Hygogg might be a blue machine, but its arms, claws, and legs are very similar to Ruby Weapon.
Final Fantasy VII Remake will be released for PlayStation 4 on April 10, 2020.