Ranpo is a genius adolescent with exceptional deduction skills. A child who grew up being bewildered with society, Ranpo is later persuaded by Fukuzawa that he is special due to an ability he possesses, which he uses from then on to solve cases together with Fukuzawa's protection and guidance.
Fukuzawa is a lone wolf bodyguard with mastery over martial arts and swordsmanship. After taking Ranpo in his stead which loses his job as a bodyguard, he establishes the Armed Detective Agency with Ranpo