I was looking for a joke along the lines of "that's why the world he depicts is so cruel, and that's why he kills characters so often", haven't found it, and by this comment am adding it.

On a serious note, whatever tool does not distract you while writing fiction is best. Usually you don't need an IDE for that.

OTOH a saga of that size might benefit from cross-referencing, timeline, etc IDE-like tools. Stephen King is known to employ a special person who checks his works for consistency with previous works in the same universe.