According to game's producer and graphics/visual artist Daisuke Ishiwatari in a 1998 interview featured in The PlayStation (JP) magazine, he stated that he loved the light fantasy world featured in the Shonen Jump manga Bastard!! and wanted to make the setting of Guilty Gear similar to it, leading to Ishiwatari coming up with many different ideas that would further the game's development.
Contributed by ProtoSnake
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According to the game's producer and graphics/visual artist Daisuke Ishiwatari in two 1998 The PlayStation (JP) and Dengeki PlayStation magazine interviews, Ishiwatari stated that he originally wanted to ask Koichi Yamadera to voice Sol Badguy, but didn't give him the role. The high cost of hiring Yamadera meant there would not be enough payment for the rest of the game's voice actors who had already been set for their roles, meaning the team couldn't make any further adjustments, so Ishiwatari took on the voice roles of Sol Badguy and Potemkin himself. When asked why they could not have just hired a different voice actor, Ishiwatari responded:

"Well, that was an option too, but I felt like if we couldn’t have Yamadera, I might as well just do it myself. Now I kind of regret that choice, it was a bit impudent of me."
Contributed by ProtoSnake
According to the game's producer and graphics/visual artist Daisuke Ishiwatari in a 1998 The PlayStation (JP) magazine interview, he was asked how the game's development started? He responded:

"Well, at the time we wrote the initial planning documents, the decline of 2D versus fighting games had not yet begun. And I personally felt like there was not a single fighting game out then that had truly “cool” characters in it, though I had been a fan of the original 2D fighting game, Street Fighter II. Anyway, feeling dissatisfied, I started drafting the plans that would become Guilty Gear. Arc System Works then publicly announced it, along with the characters, but there followed a very long period where nothing happened… eventually we reached at point at the company where we had a software development environment capable of handling it, and that’s when the real development finally started."
Contributed by ProtoSnake
According to game's producer and graphics/VA Daisuke Ishiwatari in The PlayStation (JP) magazine interview, he was asked how long did it take to make the game? He responded:

"Once we got down to the actual development work, it took about a year and a half to complete. It was a very long interval, though, from the time we finished the planning docs to the time we started development."


He also revealed that the game was originally in development for the Nintendo 64, the Sega Saturn, and for arcades as well as the PlayStation, and that as a result, Ishiwatari put a lot of thought into designing the Instant Kill system, and that it only ended up the way it was in the final game when the team decided to make Guilty Gear exclusive to home consoles.
Contributed by ProtoSnake
Guilty Gear was originally meant to use 3D models instead of the hand-drawn sprites the final version used.
Contributed by TailsFiraga
The prototype version of Guilty Gear featured many differences in the characters' appearances and weapons. Most notably, May and Potemkin are shown to be wielding large axes.

In the final version, May uses a ship's anchor, and Potemkin fights hand-to-hand.
Contributed by TailsFiraga
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Sol Badguy's Instant Kill move, "All Guns Blazing", would later be used by the EX version of the "Order-Sol" character in Guilty Gear XX Slash. Order-Sol also has an identical move-set to this game's version of Sol, and borrows this game's mechanic of charging up energy for special moves.
Contributed by TailsFiraga