Hirokawa is the leader of a cabal of Parasites which counts Reiko and Goto among its members. The group attempts to accrue political power in order to set up safehouses where they can take their victims, killing and eating them in secret. Hirokawa gains election to the office of mayor in East Fukuyama City, a small town (by Japanese standards) of 500,000 people close to Shinichi's hometown. Hirokawa wins by running on a campaign centered around locally-based environmentalism. Secretly, Hirokawa is a radical environmentalist who believes that the Parasites' purpose is to cull the human population, standing one step above them on the food chain.
He is actually a human and dies being shot by the military who suspect of him being a parasyte.