Some things I'd like to develop...

Classes

• Fighting Men - Demon Hunters/Samurai (catch-all warriors).
• Psionnes - The "magic" users Those who specialize in mastering psionics.
• Hybrids (Elves in Swords & Wizardry) - partially mutated humans who will inevitably "turn" but have a wide range of abilities that they can use to help the humans in the meantime.

Settings and Societies

• A spirit city populated entirely by ghosts.
• Lairs for the spheres and spawn points from which their monstrosities emerge.
• City of the damned - a city that has been completely "turned" (e.g., mutated/corrupted) by a sphere.
• Pockets of unreality that have emerged on the planet.
• Roaming warlord tribes.

Monsters

• Re-animated dead (including prehistoric creatures).
• Mutants (all types).
• Unterrestrial (totally new/alien to Ketoru).
• Spirits/Demons (in the Japanese sense).
• Kaiju (Referred to as "gods").

Other

• Tips of forming hunting parties, what type of roles need to be filled.
• Gazetter-style updates on sightings of the Spheres, monsters, treasures, astronomical observatios relating to the Spheres' appearances and the coming supernova, etc. for adventure hooks.
• Possible history of Ketoru and where some of the re-animated originate from.