For every one-shot like Studio Ghibli's body of work that exists, there are plenty of anime movies that follow certain series. While many of these are non-cannon, there are plenty of films that have happened in their series in one way, shape or form.
A good example of the former are most of the older Dragon Ball Z movies, with the latter being a much more recent affair and best exemplified by the Demon Slayer: Mugen Train movie.
Simply put, there are a vast amount of contemporary anime movies that do have significance to their series. This article will go into five that are completely canon to their stories, and five that aren't. The specific focus is on the how and why these anime movies are canon.
Disclaimer: As with everything, this list will contain plentiful spoilers for the anime movies themselves and the series they're based in. Opinions are subject to the author, while the opinions of the creators are included likewise.
5 anime movies that are canon, and why
1) Naruto: The Last and Boruto: The movie
Both of these Naruto anime movies come courtesy of Masashi Kishimoto. While he played a large part in the making of The Last, he took a larger role in the handling of the Boruto movie by handling the script, character designs, and screenplay.
According to Kishimoto, these projects were so monumentous that he required help from other staff members, such as the writer Ukyō Kodachi and director Yamashita.
Why these two anime movies are the only canon ones is easily explained: they are the only two to depict concrete events that happened in series. Naruto: The Last covers Naruto and Hinata getting together, while Boruto covers Boruto's first real adventure post-Naruto. The two anime films connect and show how far and wide the Otsutsuki Clan reaches, and how the heroes deal with that.
2) My Hero Academia: The Two Heroes, Heroes Rising, and World's Mission
All three My Hero Academia anime movies made it onto the canon list, despite some controversy with Heroes Rising. Kohei Horikoshi himself has already said Two Heroes might as well be canon since it contains a significant chunk of All Might's backstory.
Heroes Rising has been controversial since Bakugo gained One for All to help defeat Nine, and was originally going to be the end of the series. To many fans, World's Mission should've been a part of it proper due to the scale of events.
So, why and how are these three anime films canon? The first, as stated, covers All Might's backstory and significant people in his life, and had an episode dedicated to previewing it before the Forest Traing camp arc.
Heroes Rising contained the first onscreen appearance of Hawks. World's Mission not only got an episode previewing it during the Endeavor Agency arc in the anime, but also dealt with quirk enhancing Trigger drugs, the Quirk Singularity/Doomsday theory, and involved everyone around the world.
3) Sailor Moon Crystal: Eternal and Cosmos
Just like Dragon Ball Z, the prior trio of Sailor Moon movies aren't canon to the series. The reboot Sailor Moon Crystal rectifies that by having the last two arcs be played out in movies. While Cosmos is months away at the time of writing, there's more than enough to say these anime films are canon to the reboot, alongside Naoko Takeuchi supervising production.
Simply put, both films are adaptations of the latter two arcs of the Sailor Moon manga. Eternal adapted the Dream arc, which saw the Inner and Outer Senshi fighting off the evil Queen Nehelenia and the Dead Moon Circus.
Cosmos will adapt the final arc of Sailor Moon, where everyone must put it all on the line to face the galactic tyranny of Sailor Galaxia and her master Chaos. Fans are forewarned that there's plenty of death to come in Cosmos.
4) Dragon Ball Super’s movies (Battle of Gods, Resurrection F, Broly, and Super Hero)
A striking change from Dragon Ball Z where most if not all of the anime movies are not canon, Dragon Ball Super entered swinging with Battle of Gods and didn't stop. Not only are all four films considered canon via the presence of Akira Toriyama doing the stories and screenplays, but the first two are canon by virtue of the anime adapting them into the series.
Battle of Gods introduced Beerus and Weiss, plus the concepts of the Gods of Destruction, Angels, and Super Saiyan God into the Dragon Ball canon. Resurrection F is Frieza's comeback, and subsequent smackdown at the hands of an ultra powerful Goku and Vegeta.
Broly is self-explanatory, introducing the major fan-favorite into the official canon. Super Hero gives Gohan and Piccolo a much-needed power boost, plus revives the Red Ribbon Army and Cell.
5) Demon Slayer: Mugen Train
Featuring one of the cleanest animations of the modern day anime movie rush, Demon Slayer: Mugen Train is a direct sequel to the second season of the anime. Despite the creator not being involved, series producer Yuma Takahashi wanted to continue production of the series with studio Ufotable. It was determined that a film would be appropriate considering the shortness of the Mugen Train arc.
The anime movie covers an extremely short 15 manga chapter arc wherein Tanjiro, Zenitsu, and Inosuke are all stuck aboard a demonic train. First, everyone falls asleep thanks to a spell, which leaves them vulnerable in their dreams. It only gets crazier from there. The anime movie is canon owing to Kyojuro Rengoku's presence, and Tanjiro learning Flame Breathing.
5 anime movies that aren't canon, and why
1) Bleach: Fade to Black
Bleach has plenty of anime movies, five to be precise. All aren't exactly canon per say, considering that they're not quite mentioned in the anime's continuty. Though Tite Kubo may have had more of a hand in Hell Verse then the other movies, the movies are officially considered non-canon and mainly service as fun one-off adventures and what-if scenarios.
For this particular entry, the anime film Fade to Black will be covered. It's arguably one of the more popular in Bleach's aresenal, so it deserves a spot. As much as a film regarding Rukia being erased from everyone's memories would've caused ripples if it was made canon, an explosion destroyes Seiretei in Soul Society, and that would've caused problems down the road if it wasn't rebuilt quickly.
2) Yu-Gi-Oh! Bonds Beyond Time
This is a weird one to explain since Yu-Gi-Oh! has multiple timelines going on. To be specific, Yu-Gi-Oh! has many different branches, but there are two main ones: anime and manga.
If the original manga timeline, as set by the late series creator Kuzuo Takahashi, is followed, then Bonds Beyond Time is not canon. The reason being is that the manga breaks off from the anime following Pegasus' death at the hands of Bakura after the Duelist Kingdom arc, which was averted in the anime.
What Bonds Beyond Time depicts is a celebration of the Yu-Gi-Oh! anime 's 10th anniversary, featuring Yu-Gi-Oh, GX, and 5D's crossover. It's very obviously not canon considering the time travel aspect was not mentioned by either of the three series it crosses over.
Instead, it's an awesome time travel movie featuring main protagonists Yugi Moto, Yusei Fudo, and Jaden Yuki chasing a villain named Paradox. Their individual realities begin to vanish owing to Paradox's meddling with the timeline.
3) Hunter x Hunter: Phantom Rouge
Hunter x Hunter has two anime movies of its own that are non-canon, one of which being the film Phantom Rouge. While it did have a manga prequel in the form of the Kurapika Recollection, the events of the film are not entirely canon to the series.
This is despite the fact that the film's plot is based on an unpublished story creator Yoshihiro Togashi wrote around 10 years earlier, and Togashi did have some creative input.
The plot of this anime movie involves the characters of Leorio and Kurapika investigating a rumor of a boy having red eyes with the hope of locating a Kurta relative. The trip leaves Kurapika with his eyes stolen, so Gon and Killua journey to help him retrieve his eyes. The film may not be canon owing to how events are structured, but the inclusion of his backstory is.
4) One Piece: Z
Regarding One Piece, none of the anime movies are regarded as canonical save for arguments made for Shining World and Red. The latter two are considered the most canonical due to manga creator Eiichiro Oda's direct involvement in them, yet arguments crop up repeatedly involving the details of where and when the film takes place.
As for the plot of One Piece: Z, the former naval admiral "Black Arm" Zephyr stages a raid on Marine naval bases on Firs Island. He stole the Dyna Stones, caused a massive volcanic eruption with one of them, and destroyed Firs Island.
The story moves between the Marines attempting to recover their property, Z attempting to trigger a massive eruption that'll end the New World, and the Straw Hats trying to stop him.
5) Lupin The Third: The Castle of Cagliostro
While Lupin The Third: The Castle of Cagliostro is considered Hayao Miyazaki's feature-length directoral debut, it's in the style of older anime movies based on the series.
None of the several Lupin III films or specials feature any continuity with any of the five TV series, any of the other films, or even the manga. Standing alone is what makes them work so well for many watchers, with many feeling these anime movies are timeless, even with outdated styles and clothing.
This classic film follows the gentleman thief Arsène Lupin III and his crew as they successfully rob a casino and find it full of counterfeit money.
Tracking it down leads them to the small country of Cagliostro and, ironically, the thieves end up on the trail of a larger money counterfeiting and a forced marriage operation. Lupin and his nemesis Inspector Zenigata team up to escape the labyrinthine castle and save Princess Clarisse from Count Caligliostro.
These are five anime movies that are canon, and five that are not. It's worth noting that they are all worth watching, even the non-canon ones. Films have changed over the course of their existence, and contemporary ones being canon may become the norm over the next few years.
If any anime movies were missed that fit either category, readers are encouraged to add their own picks in the comments.