One thing about anime that fans can either love or hate is filler. Filler is what happens when the anime catches up with the manga. So in order to avoid a hiatus or the possibility of being canceled an anime series will create filler so the manga can have more time to produce more content.
The creation of filler also leads to the concept of non-canon in anime. Non-canon is content that is anime exclusive, meaning that the content isn't in the original manga making it non-canon. Filler can either add more depth to the show or completely miss the mark and make fans want to skip all filler.
10 Sailor Moon: Makai Tree Arc Adds Depth To The Show
Season 2 of the original Sailor Moon also known as the Makai Tree Arc is surprisingly non-canon. In this season, Usagi Tsukino's memory has been wiped, and she's now back to living her normal life. However, there has been an emergence of a Maki tree and two aliens know as Ali and An. In order to get rid of these new aliens, Luna has no other choice but to reawaken Usagi's memories.
Many fans consider this arc to be canon since it adds so much depth into the show, for instance, things like Usagi's new transformation, how they got their memories back, and the moon rod.
9 Naruto: Three-Tails Appearance Is Skipped By Most Fans
The Three-Tails Appearance arc in Naruto is a non-canon arc that is often skipped by most fans. This arc is whopping 16 episodes that goes into great detail about how Kabuto Yakushi and team Guren are instructed to capture the vessel that holds the three-tailed beast.
In the manga, we do see this part of the story but it is very quick and fast. However, the anime really draws this arc out making it a drag. Fans recommend skipping this arc since the only interesting part is that Naruto uses cool new ninjutsu that we never see again in the anime.
8 Noragami: Rabo Arc Only Lasts Two Episodes
Although the Rabo arc in Noragami only lasts two episodes (11 & 12) it is still non-canon. In these two episodes, a God that used to work with Yato appears and tries to convince him to go back to his old ways as a Calamity God.
Rabo's sudden appearance is the true test to see if Yato has really changed for the better and at the end of the season, we see an epic battle between the two. Fans speculate that the reason this was added into the series was that there was a lack of battle in the anime and the studio wanted it to end with an epic one.
7 Fairy Tail: Fans Either Love Or Hate The Eclipse Celestial Spirits Arc
Fairy Tail is another anime that has a significant amount of filler. One arc that is non-canon is the Celestial Spirits Arc, this arc is one where fans either love or hate it. In this arc, the twelve zodiac gates are not responding to their summoning while their appearances and attitudes have changed significantly.
This arc is filled with fights between the guild the members and the zodiac gates however, some fights can't really be considered a fight. Fans are indifferent about this arc because the tone from the beginning was very serious.
6 My Hero Academia: The Internships Arc Blends In With The Rest Of The Show
My Hero Academia hardly has any filler, however, it does have the internship arc. In this arc, fans get to see some of the 1-A during their internships. This arc has so many fun moments such as Bakugos struggles being an intern with Best Jeanist and Tsuyus's intern adventures at sea.
Anime watchers wouldn't even know this arc is non-canon since it blends so well into the actual series by adding so much depth into the side characters.
5 Soul Eater: The Ending Arc Was A Dissapointment
The ending of Soul Eater is non-canon and completely different from the manga. Many fans can't help but feel disappointed with how the anime ended things. The final battle between the Maka and the Kishin showcases Maka being half weapon- which is something never mentioned in anime at all.
And fans never get to see if Soul was ever able to become a Death Scythe- something the anime focused heavily on in the beginning. Overall, the ending of the anime cut out and changed so many things from the manga.
4 Black Butler: All Of Season 2 Was Filler
Season 2 of Black Butler is entirely non-canon and is often skipped by fans. Season 2 introduces two new characters, a new butler and his young master, these two characters are nowhere seen in the manga and are completely non-canon.
Of course, the only reason this season exists is that the anime caught up with the manga and needed to add filler. So fans, recommend skipping this season and continue on the Book of Circus arc.
3 Inuyasha: All Of Season 4 Is Filler
Season 4 of Inuyasha is non-canon however one can hardly tell. In this season Kagome and Inuyasha continue their journey through feudal era japan to defeat the evil demon Naraku and collect the shards of the Shikon Jewel.
Anime-only watchers wouldn't know that this season is non-canon because it does a good at staying true to the animes story and furthering the development of all the characters.
2 One Piece: G-8 Arc Is Considered Canon By Fans
One Piece is a pretty lengthy anime that hardly has filler, but one of the most notably non-canon aspects of this anime is the G-8 Arc. In this arc, the straw hat lands in the middle of a marine base G-8 so the crew makes their way through the base to reclaim the Going Merry and avoid getting captured.
Many fans consider this arc to be canon and recommend others to not skip it because it follows the storyline and develops the character's personality further.
1 Bleach: Zanpakuto Unknown Tales Arc Is Filled With Plot-Holes
The Zanpakuto Unkown Tales arc in Bleach is one of the few non-canon arcs in the series. In this arc, being lead by Muramasa the shinigami's Zanpakutos start to take human forms and turn against their owners. Bleach fans have noted that this arc is filled with plot holes that don't line up with the rest of the canon arcs and often contradict the rest of the story.
Therefore, it is recommended that fans skip this arc to avoid confusing themselves with the story.