Filler, Canon and Mixed Anime Episodes Explained

You are deep into a long anime, fully hooked, when the next episode starts and something feels off. The villain has vanished. Last week's cliffhanger is never mentioned. The whole cast is suddenly enjoying a quiet day like nothing ever happened. So you check the episode number. Then the title. Then you wonder if you clicked the wrong episode.

I did exactly this when I started watching anime, because nobody had told me about filler episodes. If that sounds familiar, this guide explains filler, canon and the in-between kinds in plain words.

What are filler episodes in anime?

Filler episodes are anime episodes made for the TV show that are not in the original manga. Studios usually add them when the show gets too close to the manga's story, so the author has time to write more. Canon episodes follow the manga. Mixed episodes contain a bit of both.

"Canon" simply means the official story, the one the original creator wrote. Most anime come from a manga (a Japanese comic), but some come from light novels (illustrated story books) or original ideas. This guide mostly says "manga" because it is the most common source, and the same ideas work for the others.

The four kinds of anime episodes

Fans sort episodes into four groups. These labels are made by fans and tracking sites, not studios, so two lists can disagree about a single episode.

Manga canon

These episodes follow the manga story. The events, characters and order of scenes come from the comic, even if the anime stretches a scene a little. If you want the story exactly as the author told it, these are the episodes.

Mixed canon/filler

Part of the episode comes from the manga and part is made up for the anime. The extra part might be a new scene, a longer fight or a side character who is not in the comic.

Many fans watch these episodes, me included. The manga part still carries real story, and skipping it can mean missing small details. Some scenes inside are filler, but it is rarely a problem, since they usually fit right into the story.

Anime canon

These are episodes that are not in the manga but are meant to be part of the anime's own story. Think of them as extra chapters written for the anime. The original creator usually approves or guides them, which is why they feel like a real part of the story.

Because of that, they are not the same as filler. Filler lists keep them in a separate group, and many viewers watch them, me included. A few guides call them optional, since the manga never had them, so the choice is yours.

If the creator was not involved, fans are more likely to call such episodes filler. Fans do not always agree where anime canon ends and filler begins, so a filler list on a tracking site is the safest way to check.

Filler

Filler is anime-only content that does not move the main story forward. It is usually a standalone adventure or side story written by the anime's staff, not the manga's author. Some are silly, some are sweet, and a few are well liked.

Here is how it looks in a real series. In the original 220-episode Naruto, fan lists mark about 74 episodes as manga canon, 56 as mixed and 90 as filler. The big filler stretch runs from about episode 136 to 219, with episodes 141 and 142 marked as mixed in the middle.

Naruto's anime started while the manga was still being written, so it had many more gaps to fill than a finished story would. Lists differ slightly, so treat these numbers as round figures.

Why are there four types?

Because turning a comic into an anime is not all or nothing. Some episodes come straight from the manga, some are brand new, and some sit in between. Fans made one label for each, and each answers a simple question: did this come from the original story, and does it matter to the story?

How do filler episodes get added?

Here is the usual path.

1. The anime airs every week on a fixed schedule, while the manga is still being drawn a few chapters at a time.
2. The studio can make episodes faster than the author can write new story, so the show gets close to the end of the manga.
3. The team picks an option: add filler, stretch scenes to slow the story down, take a break, or write its own arc (a long storyline) or ending.
4. Anime staff write any new episodes, since the manga's author is busy with the manga.

One well-known case is Fullmetal Alchemist (2003). It caught up with its manga, so the studio wrote an original ending, and the manga's author asked for it to be different. Fans still enjoy comparing it with Fullmetal Alchemist: Brotherhood (2009), which follows the manga all the way through.

Many newer shows avoid the problem by airing in seasons with breaks, so the manga can get ahead. One Piece took a long break from October 2024 to April 2025, and from April 2026 it airs up to 26 episodes a year in two blocks. The change is meant to keep the anime in step with the manga, and some fans expect less filler as a result.

Should you watch filler episodes?

There is no right answer. It depends on your taste and how much free time you have.

I first ran into filler somewhere in the middle of Naruto, back when I did not even know the word. Once I learned which episodes were filler, I still never skipped them. I have watched filler in almost every anime I have seen, and some of it turned out to be pretty good. When I want to save time, I play it at 1.5x to 2x speed. If I ever did skip something, filler is the only kind I would pick.

If you want to experience more of an anime, filler gives you extra time with the characters and their world. If you only care about the main story, skipping it is a good choice too. For Naruto, fan lists say no filler episode is needed to follow the main plot.

Common questions about filler and canon episodes

How can I tell an episode is filler while I am watching?

There are clues: the main story pauses, the last cliffhanger is ignored, or a standalone adventure shows up. These are only hints, though. A filler list on a tracking site is the easiest way to check.

Why does filler ignore what just happened?

The real story is still being written in the manga, so filler cannot move it forward. It usually presses pause and tells a side story instead.

Is filler canon?

Not in the original story's sense. Filler is not part of the author's story. The exception is anime canon, which the creator approved or guided.

Do all anime have filler?

No. Attack on Titan's main TV episodes are listed with no pure filler, and Fullmetal Alchemist: Brotherhood is usually described as having none, because both follow their manga closely. Demon Slayer also follows its manga closely, with just one anime-original episode: the first episode of the Mugen Train TV arc, a prequel that happens just before the main story. Some shows also add small anime-only scenes inside regular episodes, which lists usually do not count as filler.

Does this apply to anime based on light novels?

Yes. The same labels work, and "manga canon" simply means following the novel instead. The original story is the book, not a comic.

Once you know the four labels, that mysterious episode stops being a surprise and becomes a side trip you can enjoy or skip.