My favorite Japanese monster never took off to cult status. A rip-off of
The Blob, the 1959 movie
The H-Man among its other virtues titillated (buttilated?) with an unusual amount of female undress for the time. It set my heart thumping although, 9 years old at the time, I wasn't sure why.
Never saw the H-Man, but G-Fan magazine had a big article on it a while back. I forget the issue, but it was quite detailed.
It sounded pretty interesting, and the photos with the article depicted some very attractive ladies.