Gensai acts as antagonist Chin Chin Chou's principal bodyguard and enforcer, a highly skilled ninja exhibiting exceptional strength, speed, and combat prowess. His most defining characteristic is an unexplained, seemingly supernatural ability to repeatedly recover from fatal injuries – including gunshot wounds to the head – reappearing unharmed shortly after apparent death or incapacitation. This extreme resilience fuels the implication, supported by dialogue stating "Gensai's not one man," that he might not be a single individual, potentially using ninja clone techniques or employing body doubles to create an illusion of invincibility and multiple lives.

His unwavering loyalty belongs solely to Chin Chin Chou, whom he consistently accompanies. Gensai engages directly in violent confrontations against Lupin III and his associates throughout their pursuit of the golden dragon statue. He participates in direct combat, ambushes, and employs deception, such as disguising himself as a fortune teller in an assassination attempt on Goemon Ishikawa XIII. He subdues Fujiko Mine during a shower scene and later assists Kikyo in restraining Lupin, Jigen, and Goemon using a shadow pin technique during a rescue attempt.

Gensai meets his definitive end during the story's climax. After numerous apparent deaths and reappearances, he is finally killed in a final confrontation with Lupin III. The narrative resolves the mystery of his multiple returns by presenting this defeated version as the "last" Gensai. His role remains strictly that of a persistent and physically formidable antagonist serving Chin Chin Chou's interests until this ultimate defeat.