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My plan for Berserk was that Miura would complete it sometime when I was in my late 50s, whereupon I'd sit down regularly to go through it all, starting from scratch.
Of course, that wasn't gonna happen, because Miura was an obsessive perfectionist who worked himself to the bone, on the art at least. See the spiny ridged tentacles in the foreground here? No shortcuts or shit here, he sat down to do all of this, hence why the manga took so much time, even when he did use digital tools, he'd still go down to pixel by pixel to get it just right (which is often kind of how I sprite, actually, except my scale of work is tiny).
Apparently quite a lot of the story and setup was kind of made up as he went, which is amazing for how good the entire era with the Band Of The Hawk was, but would also explain some of people's complaints about later parts, like being stuck on a boat (I haven't read that far, so IDK what the complaints are). Apparently he had some ideas jotted down and had a vague plan for where he would take it all, no idea how much was actually left, or if he wrote down all of his actual ideas.