In Seven Deadly Sins, when Gowther and Dreyfus fought, Gowther saw into the mind of Dreyfus and Dreyfus was already being controlled by one demon.
Why was Gowther not able to see the demon?
In Seven Deadly Sins, when Gowther and Dreyfus fought, Gowther saw into the mind of Dreyfus and Dreyfus was already being controlled by one demon.
Why was Gowther not able to see the demon?
As the latest chapters (303 to 305) indicate, whenever a battle occurs in character's mindscape, what happens is entirely controlled by the most "willful" of the two fighters.
Gowther's Invasion magic lets him wander freely through most characters' subconscious, as long as they are weaker than himself. However, the demon within Dreyfus (Fraudrin) is vastly stronger on all counts than Gowther. According to the artifact Balor's Eye, Gowther's strength of will was quantified at 1300, whereas Fraudrin's was numbered at a whopping 3000.
The power discrepancy means that Fraudrin could bar Gowther from seeing his true form, or learning any information for that matters. He instantly overwhelmed him and forced Gowther out of Dreyfus' mindscape (whose strength of will was 1000). Keep in mind that any event occuring within is a character's mindscape is a literal battle of wills ; and that it is mostly abstract concepts and spirits shaped and drawn in understandable ways for narrative convenience.