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.
The Kaiju No. 8 manga is mainly about a character's struggle and growth in a kaiju-infested world. It has elements of action, adventure, and mystery. The plot keeps you on the edge of your seat with unexpected twists and turns.