Genpei Ōtaguro, also known as Genpei Hirukawa, is an escaped convict responsible for at least six rape and burglary offenses. In one criminal instance, he invades the home of an affluent couple, Yasuhisa and Tokie Jinnō. He restrains and beats them both, then forces himself on Tokie repeatedly—both while she is conscious and unconscious—in full view of her bound husband. After looting their safe, he departs.

The assault leaves Tokie pregnant, and she later gives birth to a son, Tatsuya. Yasuhisa, mistakenly convinced his wife took secret pleasure in the violation, subjects both her and the boy to years of abuse, certain the child is not his own. The unrelenting cruelty eventually drives Tokie to take her own life.

For many years, Genpei continues as an active serial offender, abducting, raping, and murdering victims such as cheerful bicycling schoolgirls. His methods characteristically involve anal rape and fatal strangulation.

Years later, Genpei reunites with his adult son, Tatsuya, at the son’s mansion in a moment of dark family connection. The encounter culminates in Genpei and Tatsuya compelling one of their captives to perform a bestiality act with a German Shepherd. Genpei then rapes and strangles the victim to death simultaneously as Tatsuya observes. This solidifies a lethal partnership between father and son, who join forces to perpetuate their brutal and depraved crimes.