As lengthy anime like Boruto continue full steam ahead in the winter airing season, fans enjoy the original content and remember that with shows like this, that's sometimes a rare treat, as much of their runtime can consist of anime-only filler episodes where there isn't enough manga content to adapt.
Because they usually aren't relevant to the main plot, fans tends to look down on filler episodes, or worse, full arcs of filler. But if a filler arc is well-done enough, such as in Bleach or Yu-Gi-Oh!, fans will not only love them but often forget that they're filler at all.
Zanpakuto Rebellion Arc (Bleach)
Almost half of Bleach’s 300-plus episode runtime consists of filler, and while most of it is average, the one filler arc that stands out among the rest is the Zanpakuto Rebellion Arc, in which, as its name implies, the Zanpakuto spirits residing in the Soul Reapers' weapons come to life, revolting against their wielders' control.
"People talk [trash] about how much filler Bleach has," asserts a Redditor whose account was deleted, "but the Zanpakuto Rebellion was great." Fans have a lot of fun with this arc for the several new and interesting characters it introduces and the top-notch animation given to the battle scenes.
Rabo Arc (Noragami)
As Redditors like Vaxivop point out, "The last few episodes of Noragami were very well done, even for filler." After Yukine’s successful ablution, Yato still has to deal with the demons of his past in the form of anime-only villain Rabo, whose plotline finishes the first season in place of the then-incomplete next story arc in the manga.
In addition to raising the emotional stakes for Yato and Yukine by erasing Hiyori’s memory of them and forcing them to fight to get it back, Rabo also reflects what Yato would be if he didn’t have his connection to his friends, who support him and bolster his desire to do good: a brutal god of war and calamity capable of nothing but bloodshed.
Other World Saga (Dragon Ball Z)
Dragon Ball's filler arcs aren't usually much talked about, though the filler episode where Goku and Piccolo learn to drive is a fan favorite! However, the Other World Saga is considered so good that some fans, such as Redditor Grafical_One, believe it to be "better than the actual ending."
After the Cell Games, viewers get to watch the exploits of the deceased Goku into the afterlife, where he helps King Kai subdue several past villains who have been causing trouble in Hell and then eagerly takes part in another tournament with other deceased warriors, with the prize of personal training from the Grand Kai.
G-8 Arc (One Piece)
Despite being one of the longest anime ever to air, One Piece surprisingly doesn't have too much filler in its hundreds of episodes. What it does have deeply impresses fans, to the point that Redditor jtyti15 "didn't even realize it was filler till I looked into it later."
This action-packed story lands the Straw Hats in the middle of a Marine base, forcing them to outsmart and outfight their worst enemies, including Jonathan, a student of Admiral Akainu, one of One Piece's most powerful villains. Fans love all the strategies that the cast employs to evade capture, especially Shepherd's brief stint as Condoriano.
Battleship Phase (Hunter x Hunter 1999)
The first adaptation of the original manga adds another phase to the Hunter Exam Arc. Before the examinees can get to Zevil Island, they need a boat strong enough to take them there through the approaching storms. Friends and enemies alike all work together to get an old battleship operational and across the treacherous ocean in one piece.
Redditor FlameDragoon933 explains that the arc simultaneously "feels like an adventure game premise" and has "its vibes fit so well with HxH's fantasy/slightly bizarre world. The exam doesn't feel out of place too, since cooperation is a useful skill to have in the real world." It's another example of filler that slots in perfectly with the manga's content.
Waking The Dragons Arc (Yu-Gi-Oh!)
Taking up the majority of the original Yu-Gi-Oh! Duel Monsters series' fourth season is this fan favorite arc. New villain Dartz and his loyal followers believe that the world is an inherently evil place, and, using the Seal of Orichalcos cards to steal the souls of anyone they defeat in a duel, seek to destroy it completely.
Redditors such as Tumor159 call Waking the Dragons "the best arc of them all," with its consistently good duels showing off flashy new cards and its heightened emotional stakes. "Fate of the Pharaoh, Part 3," in which Yugi sacrifices himself to keep the Seal of Orichalcos from stealing Atem's soul (which only happens because Atem himself played the card in his drive to win) is one of the saddest Yu-Gi-Oh! episodes.
Key Of Starry Sky Arc (Fairy Tail)
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Redditor Aniboy43 chooses this arc as their favorite because "it was just creepy and weird in terms of direction and storytelling," which is a departure from Fairy Tail's usual upbeat and adventure-oriented tone more in line with its fellow shounen anime.
When Lucy is presented with a clock hand from a strange young girl, she and the rest of Fairy Tail are dragged into conflict with the cult of the Zentopia Church, who pick fights with them over the parts of the rest of the clock. The guild rushes to collect all the parts before Zentopia does, but are met with a nightmarish shock when the clock is finally put together.
Kakashi ANBU Arc (Naruto Shippuden)
Naruto and Naruto Shippuden might be the anime most well-known for its massive amount of filler content. While some arcs and episodes are especially maligned, many others are fan favorites, containing some of the best villains in Naruto. Especially popular among them is the arc focusing on Kakashi's past exploits in the Leaf Village's ANBU Black Ops.
Standing out even to Redditors like IISuperSlothII who says they "generally go out of my way to skip filler," this arc sees a younger Kakashi attempting to get over the trauma of Obito and Rin's deaths by devoting himself to ANBU missions: investigating Orochimaru's crimes, clashing with the organization Root, and working alongside Itachi Uchiha before his defection.
Saga of Asgard Arc (Saint Seiya)
Adapted from one of the most expensive out-of-print manga, Saint Seiya's anime-only content is highly regarded too. The Asgard Arc has Redditors like jorgesama99 still praising it as being "very well written with characters having real motivations and personal developments even better than in canon sagas."
One of the oldest filler arcs in anime history, coming from a show that aired from 1986 to 1989, the Asgard Arc introduces, naturally, the harsh and formidable land of Asgard. The kingdom's priestess Hilda is compelled by the gods to summon the God Warriors, equal in power to the Saints, and continue Asgard's old ambitions of world conquest.
Final Arc (Fullmetal Alchemist 2003)
Famously or infamously, depending on who you're talking to, the entire final arc of the 2003 adaptation of Fullmetal Alchemist was original content, due to ending long before the manga was complete. In place of Father, the main villain is Hohenheim's ex-lover Dante, and in foiling her plans, Edward winds up restoring his brother's body but stranding himself in World War II-era Earth.
Redditors like taximan230 and this deleted account maintain that the entire show is some of the best filler of all time, and while filler episodes are dotted throughout 2003, this ending is the primary filler arc. Some fans find it nonsensical and unsatisfying, especially because it separates the Elric brothers, but others love it for its intensity, creativity, and emotional weight.