There's no sense trying to define a plot for Tetsuo: The Iron Man. It's essentially a series of very 80s experimental video shorts strung together into a very loose thematic structure. One man chooses to inject himself with metal, while another transforms into metal. That's the nuts and bolts.
Writer/director Shin'ya Tsukamoto (who also stars as the "Metal Fetishist") crafts a masterful body horror, focusing on the selfishness of the 1980s embodied through the rise of technology. His character willingly slices open his body and shoves in rusty rebar. While running through the streets to get help, he's hit by a business man and his girlfriend. They do stop to help, but they leave him to die. Everyone is out for their own interests and no one will help another person.
Tetsuo: The Iron Man feels like it's a museum piece in the best way possible. I've walked through many modern art museums and seen curated video art pieces just as strange and disturbing as Tsukamoto's film. The opening sequence with the fetishist, especially, is video art. The black and white cinematography actually creates more clarity in this bizarre psychological shocker, cutting through the chaos of found imagery of machines and white noise to establish the fetishist's obsession with machinery.
Once the man begins to transform, we enter dystopian cyberpunk territory. Every living person is a threat because every living person is impacted by technology. The man meets a woman at the subway who accidentally becomes possessed with a bird/machine hybrid just by investigating a strange and wondrous creature. The man's girlfriend also transforms through contact with him, creating a literal battle of the sexes through spinning steel genitalia; it's weirder than it sounds, believe it or not.
Every time the plot, however much you can claim there is, starts to linger too long, Tsukamoto introduces a new image or thematic concept to pull you back in. It's like the modern art video installation gallery installed a travelator and pulled you through the entire exhibit hall with no way to get off. It's a fast-paced 67 minute feature that doesn't overstay its welcome.
If anything, the film could have benefited from hinting at some of the perfectly off-putting live action stop motion animation effects earlier in the film. The quick cuts between ambient imagery and violent action are replaced with jerky cartoon chase sequences through the streets of the town. It's really quite remarkable how far Tsukamoto pushed the limitations of black and white 16mm stock to ape the ubiquitous home camcorder. He even split the camerawork between himself and leading lady Kei Fujiwara (the woman) to capture all of the insanity from close quarters or first person perspectives.
Tetsuo: The Iron Man is not for the faint of heart. It's gory and disturbing body horror through the sheen of Japanese cyberpunk. Those who have the stomach for it will experience arguably the greatest live action cyberpunk feature ever made.
Tetsuo: The Iron Man is currently streaming on Shudder.