I think 'One Piece' might fit the bill. Some of its filler arcs have been really engaging and even more enjoyable than certain parts of the main story.
Filler words also play a role in the development of the narrative voice. An omniscient narrator might use different filler words compared to a first - person narrator. The choice of filler words can also change over the course of the novel as the character grows or the situation changes. For instance, a character who becomes more confident might use fewer filler words as the story progresses.
In novels, filler words can also be used for character differentiation. A nervous character might use more 'um's and 'ah's compared to a confident one. They can be a subtle tool for characterization. Moreover, in some cases, filler words can be used to create a regional or social dialect. For example, certain words might be more common in a rural setting's dialogue, which can help to paint a more vivid picture of the world in the novel.
One filler horror story could be about a haunted doll. The doll was found in an old attic. It had a cracked porcelain face and empty eyes. At night, it would move on its own, and people in the house could hear faint giggles coming from the room where it was placed. Another could be a story of a cursed mirror. Anyone who looked into it for too long would see a distorted version of themselves and then strange things would start to happen around them, like objects moving on their own.
The Boruto manga is pretty straightforward in its storytelling and avoids filler. It keeps the narrative moving along without including extraneous material that doesn't contribute to the main storyline.