Discourse on Decadence is an extraction ability that allows Ango to read the memories left on materials that he touches. For example, Ango used this ability to read into the escape route of Mushitaro Oguri along with Atsushi Nakajima and Kyōka Izumi by using his ability on the ground they passed through and later on some of Mushitaro's stolen cash money while escaping. This ability may also work on humans as seen when Ango offered to read the information sent by Sigma towards Atsushi in order to figure out Kamui's location.
One downside of this ability includes causing a considerable amount of mental strain if the user had yet accustomed to it or through mental overload. Ango confirmed that he once experienced this situation when his brain temporarily surrendered consciousness in order to sort an influx of large information gained from his ability. In some cases, causing an external stimulus such as a sting or a strike may trigger a recovery from such experience.
The ability is a reference to Discourse on Decadence (堕落論, Daraku-ron?), a critique essay written in 1946 by the real-life Ango Sakaguchi, who was one of the writers notably associated with the buraiha. Aside from dissecting the essence of bushido in post-war Japanese society, he argued that a fall into decadence is inherent in humanity, which could help attain a rediscovery to and the salvation of human nature through perseverance in life rather than preservation throughout life.
- It is implied in the light novel that Ango used this ability to retrieve information from the deceased mafiosi he was writing reports on. The anime also shows Ango touching the effects retrieved from the deceased mafiosi, hinting that he was using his ability to collect information on their lives. This would explain why he was able to write about their lives on his reports merely through inspecting their belongings.