Shinjurō strongly resembles his son, Kyōjurō Rengoku, possessing unruly orange hair that flares out around his face, becoming redder near the ends above his ears, that he wears messily tied back behind his head. He has fair skin, bushy black eyebrows and angry, orange eyes that redden near the pupils, that are slanted inwards and shaped so as to give him a furious appearance. Shinjurō is a very short-tempered man, especially when regarding the Demon Slayer Corps and his deceased son, Kyōjurō.