In The Executioner, Ryuichi Koga (Sonny Chiba) is a descendent of the Koga Ninja school, now earning his living through more nefarious means as a gun for hire. When he is enlisted to take down a drug cartel alongside Hayabusa (Makoto Satô), a disgraced former narcotics detective now operating within the criminal underworld, and renegade Aikido master Sakura (Eiji Gō), tensions grow among this three-man team of ne'er do wells as each come to question each other's motives.

In The Executioner 2: Karate Inferno, when a priceless jewel owned by rich heiress Sabine is stolen, along with her daughter, Professional thief and hired killer Ryuichi Koga and his gang are hired to retrieve both. At a ransom exchange, the team save the girl but lose the money and the jewel. When Sabine decides to deal directly with the thieves and obtains the jewel on her own by paying the ransom, Koga, having been stiffed of his fee by Sabine, steals the jewel. Little does he know, it's a fake. Now, Koga and the team must break into a high-security bank to steal the real jewel.