The Human Vapor, in his humanoid form simply resembles a Japanese man, enveloped in a blue glow.
Mizuno was a former test pilot but retired after he somehow got infected and then confined to a sanitorium for a long time. He later became a librarian until Dr. Sano offered Mizuno to become a "test subject" for scientist's projects. However, the tests backfired and Mizuno became an indestructible vapor man. He then began a life of crime to try and support his wife.
In the Human Vapor's gaseous form, the Human Vapor can wrap around people's heads and suffocate them. He can also disappear into air.
- Main article: Human Vapor/Gallery.