Yisme is a Paranormal Investigator
Given that Yisme's dream world is entered through using the camera rather than sleeping, the dream world could be an abstract representation of Yisme's work. Saving at the TV is Yisme looking back over the recording(s) and saving it to video.
Yisme's field of expertise is likely some sort of investigative work into monsters/the occult/paranormal, as many of the notable NPCs look like monsters/ghosts. On top of that, many of Yisme's effects give them a monstrous or ghostly appearance. Some areas in the dream world also have graffiti on the walls, which could possibly be occult/ritual symbols.
There are also hints of Yisme being watched by another entity. One inescapable area shows Yisme being watched by many eyes along with the message "I see you". This can also be backed up by Yisme's menu title: The Stalked. An event in the game suggests that an unknown party needs Yisme to carry out some (unknown) task/plan.