In the Eternal Eden franchise, summons will draw inspiration from the Holy Scriptures rather than using demonic names or names from other mythologies.
Eternal Eden 9 is meant to have a vibe of the generation of the 32-Bit era, such as the Dreamcast, the first Playstation and also the Nintendo DS.
The release order of these games has zero importance whatsoever. Eternal Eden 5 can be released before Eternal Eden 2. Et cetera.