4 ideas
In 'The Psychological Test,' a student murders an old woman for her hidden money. He knows he will face a word-association test, so he trains himself to respond neutrally and passes. The detective Akechi Kogoro catches him because his answers are unnaturally perfect, and because he truthfully mentions a folding screen he could only have seen at the time of the crime. Preparing to defeat a detection method creates its own detectable signature.
In 'The Human Chair,' a woman writer reads a letter from an ugly furniture maker. He confesses that he built himself into a hollow armchair, secretly felt the bodies of the people who sat on him, and that the chair now sits in her study. A second letter then claims the first was only a manuscript submitted for her opinion. The reveal leaves both the character and the reader unsure which document to believe.
Rampo moved away from clean logic puzzles toward ero-guro, fiction that combines sexual obsession with bodily deformity, confinement and perverse sensation. In 'The Caterpillar,' a quadruple-amputee veteran is kept by his wife as an object of her desire and cruelty. In 'The Hell of Mirrors,' a man seals himself inside a mirrored sphere and goes mad. In this mode, horror comes from human appetite and self-made enclosures, not the supernatural.
Rampo's lasting influence on Japanese detective fiction came as much from infrastructure as from his own texts. He adopted Poe's name to signal a lineage and helped found the Detective Authors Club in 1947, which became the Mystery Writers of Japan. A genre becomes self-sustaining once someone creates a professional body, a talent pipeline and a readership that outlast any single author's style.