Mizuki's father worked for the American embassy, so he would bring home stacks of comics for his son the cartoonist to learn by. Mizuki's first work is pretty much straight-up copying American comics.
Reading Shigeru Mizuki early works, and one of them is just full-on an unauthorized (I assume?!) Plastic Man book and honestly that 100% tracks in retrospect with what I've read and loved in Kitaro.