The Deus Ex Machina (or God In The Machine) is the most controversial yet misunderstood plot device in all fiction. Simply put, it's when "god" (read: the writer) steps in to give the desperate heroes a sudden solution to a hopeless situation.
Deus Ex Machina aren't inherently bad, but when used clumsily or improperly, they can ruin even the best anime. It should be noted that these aren't unpopular plot twists and endings, but bad plot contrivances and unearned conclusions.
WARNING: Spoilers ahead.
10 Pokémon: The First Movie — The Pokémon Cried So Hard That Ash Ketchum Came Back To Life
Pokémon is no stranger to plot contrivances, but nobody minds since they give the anime its goofy charm. One of the best hilariously bad story-breaking examples came from Pokémon: The First Movie, where Mewtwo was a few steps away from declaring war on humanity and Ash Ketchum died trying to stop him.
More specifically, Ash was petrified into stone, but he was as good as dead. Just before his death could've really hit home, the surrounding Pokémon cried and their tears somehow brought Ash back to life. Mewtwo pontificated about how Pokémon and humans are actually capable of loving each other, but this didn't explain the Pokémons' magical tears, nor were they ever bought up ever again.
9 Yu-Gi-Oh! Duel Monsters — The Heart Of The Cards Broke All Tension & Logic
Deus Ex Machina in anime might as well be renamed "The Heart Of The Cards," the abstract force that helps Yami Yugi win literally every card duel he's in. In practice, believing in a card's heart somehow allows Yugi to draw the right card at the right moment. That, or it powers up the card or gives it a new effect.
The actual logic or limits of The Heart Of The Cards is never properly defined, though it's essentially Yugi's carte blanche to break the rules or even rewrite them while in the middle of playing a children's card game. As a result, what little internal logic Yu-Gi-Oh! had was broken from the very first episode.
8 JoJo's Bizarre Adventure — Jotaro Kujo Suddenly Learned How To Stop Time Better Than Dio
JoJo's is known for seemingly random power-ups, but Stardust Crusaders' final fight is egregious even by the series' standards. With no build-up whatsoever, Jotaro's Stand (Star Platinum) learned how to stop time just like the unbeatable Dio and The World could. Seconds after revealing this, Jotaro blew up a Dio who was just as confused as the audience.
The only explanation given was that Star Platinum just happened to unlock Time Stop the moment Dio slammed a road roller into Jotaro's face. Despite this coming completely out of left field and undoing Dio's established threat in seconds, a majority of the JoJo's fanbase doesn't hate this contrivance because it was so ridiculously cool and badass that no one dared question it.
7 Naruto: Shippuden — Madara Uchiha Was Defeated By The Anime's Actual Villain
For years, Madara was hyped up to be Naruto's big villain that Team Seven and every living ninja had to defeat. Madara was practically a ninja god by Shippuden's tail end, meaning only a Deus Ex Machina could plausibly beat him. In fact, Naruto mastermind Masashi Kishimoto himself admitted that this was an oversight.
Even when Naruto and Sasuke were blessed with god-tier power-ups from the legendary and barely mentioned Sage Of The Six Paths, they didn't stop Madara. Instead, it was Black Zetsu acting on orders from Kaguya Otsutsuki, Naruto's actual true evil who was rarely seen or spoken of beforehand, who did. Naruto and Sasuke were then able to quickly beat up Kaguya with their god-tier jutsu due to her lack of combat experience.
6 Bleach — Sosuke Aizen's Deus Ex Machina Were Defeated By The Heroes' Own Deus Ex Machina
When Aizen entered the battlefield of the Fake Karakura Town, he was basically a god. Because of how overpowered he was, and thanks to his endless contingency plans for literally every attack, it was impossible to defeat him. In effect, the only way to overcome Aizen's Deus Ex Machina was with even more Deus Ex Machina.
After Ichigo's new game-breaking techniques only momentarily stopped Aizen, the power-enhancing Hogokyu suddenly rejected Aizen. Just then, Kisuke Urahara's sealing spell - which he fired into Aizen via Kido earlier - took effect. This battle of Deus Ex Machina got so out of control that it was hard to take Bleach's ever-escalating stakes seriously.
5 Gantz — Gantz Decided To End The Anime Out Of The Blue
At the time of Gantz's airing, the manga was barely halfway done. The otherwise straightforward death game anime needed a concrete ending, but instead of declaring a winner and loser, it got surreal. This was achieved through the black sphere, Gantz, the anime's literal Deus Ex Machina that acted on its own whims and abruptly ended the story.
After Kei defeated the murderous Muruto, Gantz transported Kei to the day he died. While being cheered on by the dead characters, Kei stopped running from the train and faced it head-on. Gantz's countdown hit zero and it vanished, ending the anime. To this day, this is one of the most baffling finales in anime history.
4 Darling In The FranXX — Hiro & Zero Two Used The Power Of Love To Save The Universe
Darling In The FranXX's romantic endgame was always going to be Hiro and Zero Two, but the way their love's perfection saved the day reduced the dark mecha anime to a borderline farce. Long story short, Hiro and Zero Two's love was so beautiful that it embodied mankind's undying willpower to thrive and end the VIRM once and for all.
The VIRM is an ancient cosmic threat, and humanity needed more than some robots piloted by teenagers to beat them. The solution was for Zero Two - empowered by Hiro's love and their friends' support - to fuse with their mecha, Strelizia, to unleash Strelizia True Apus, a planet-sized Zero Two that blew up the entire VIRM planet.
3 Wonder Egg Priority — The Conflicts Resolved Themselves & Left The Anime In Shambles
After starting out strong, Wonder Egg Priority dropped the ball when the time came to resolve its biggest mysteries and fights. In the penultimate episode, the artificial human Frill was revealed to be behind the uptick in suicide incidents among girls for unknown reasons. Worse, she had her sights set on Ai, Neiru, Rika, and Momoe.
But in the heavily delayed finale, these core conflicts conveniently solved themselves without the cast's help. Frill just left after convincing Neiru (who's actually an artificial human) to join her, and everyone else gave up before Ai rescinded at the last minute. These simultaneously answered some of the anime's biggest questions while leaving more in its wake.
2 Sword Art Online — Kirito Is Practically A Living Deus Ex Machina
Beyond the implication that Kirito is the greatest gamer ever, almost all of his victories had no build-up or justification. When he's not defeating armies without losing a single hit point, Kirito is saved by or saves the day thanks to godsent contrivances. These robbed Sword Art Online of all stakes and emboldened the criticism that it was a transparent power fantasy.
Examples include Kayaba conveniently giving Kirito the game's admin rights in Fairy Dance's final fight, perfectly predicting how his assassination attempt in Phantom Bullet would go, suddenly knowing how to do gymnastics in Alicization, and - most notoriously - hacking/programming a dead Yui back to life in the original anime.
1 Neon Genesis Evangelion — Human Instrumentality Was An Abstract Intervention, Not The End Of The World
Instead of having Shinji Ikari resolve his angst through an earth-shattering battle like what most mecha anime do, Evangelion dropped the fights and psychoanalyzed him in a two-part clip show. Though this finale benefited greatly from hindsight, it's still one of the most infamous and most literal Deus Ex Machina ever seen in anime.
While Evangelion's last two episodes were recontextualized by the sequel movies, it's still an obvious cop-out - especially after it seemed to lead up to a biblically apocalyptic clash. This now iconic Deus Ex Machina was only made possible by the perfect storm of Gainax's financial problems and showrunner Hideaki Anno's personal struggles.