So in these filler episodes, does anything actually happen? Do the characters even acknowledge their existence in the proper episodes?
From what I gather, the fillers are separate stories that doesn't really have anything to do with the main story. Sort of like side quests in computer games. Lots of stuff can happen, but the characters are static: they will not develop new skills or change in any way, as it would be weird if the story continued from where it left in the main story, and suddenly the main character has learned new super moves from nowhere or formed a romantic relationship with one of the other characters without any explanation.