Hiroya Oku likely starts with a concept or story idea. Then, he sketches out the characters and plotlines. After that, he refines the details and adds depth to the story through continuous revisions.
I'm not entirely sure as it could vary a lot. It might be based on the 'Necronomicon' which is often associated with Lovecraftian horror. Maybe it involves a story with dark and mysterious elements, strange creatures, and a sense of the unknown.
I'm not entirely sure as I haven't read it specifically. But generally, it might be about dark, mysterious, and perhaps supernatural themes given the 'necronomicon' which is often associated with the occult in various fictional works.
One interesting story could be about the ancient and otherworldly creatures it might describe. Maybe there are tales of beings from different dimensions that have a strange and dark allure.