The anime adaptation was originally meant to be a New Game+. One remnant of this draft of the story is Hibiki starting out with Byakko, which in the game would only be possible in a New Game+. Word of God also stated that if the anime was 2 cours, they'd have had Hibiki start out with weaker demons and gradually power up during the course of the story.
In the anime, Ronaldo was originally meant to survive Megrez's final attack and show up in episode 12 to face off against Yamato. However, they abandoned that idea and reduced Ronaldo's influence on the story to handing Hibiki a USB containing data relating to Yamato's plans.