Filler episodes in a TV show often delve into the lives of supporting characters by focusing on their backstory, relationships, personal challenges, or individual growth. These episodes provide an opportunity for viewers to learn more about the supporting characters beyond their interactions with the main protagonists. They may also showcase the supporting characters' strengths, vulnerabilities, and motivations, adding depth and complexity to their personalities. Additionally, filler episodes can help to develop the supporting characters' arcs and contribute to the overall world-building of the show.