In the 'Missing Jaw Man' story, he might be a central character with a complex backstory. He could be a person who has been forgotten by society because of his disfigurement. He may have had a family, a job, a normal life before whatever happened to him. The story might unfold his journey to either accept his new state or seek a way to reverse it, all while facing the challenges and prejudices that come with his appearance.
Yes, manga can have fillers. Sometimes authors use them to flesh out characters or settings, or to give themselves more time to plan the main plot. But too many fillers can make the story drag.
The Trap Jaw's origin story often varies depending on the specific fictional universe. In some cases, it could be the result of a genetic mutation. For example, in certain monster or superhero lore, a character might develop the Trap Jaw feature due to an experiment gone wrong or exposure to some strange energy source. This gives them the distinct ability to have a powerful jaw - like mechanism that can be used for various purposes like attacking or defending.
I'm not sure specifically which 'Man with No Jaw Story' you are referring to. It could be a horror story about a man who lost his jaw in some tragic event, like an accident or an attack. Maybe it's a mystery where the lack of a jaw is a key clue to solving a crime.
The Naruto manga itself doesn't have fillers. Fillers are a common thing in anime to extend the runtime or bridge gaps in the manga's story. But the manga sticks strictly to the main plot.