Even if you think you know all the tropes, a particularly clever anime can still hit you with a plot twist that you just did not see coming. Sometimes, you look back on a show and realize that the big twist was hinted at, but other times there's no way you could have possibly predicted what the show had in store.
While anime plot twists can be both infuriating and satisfying, they always make a show more interesting. Twists commonly involve a single character or group, but occasionally, a good series will drop in a massive twist that changes everything about the plot. When viewers find out that Assassination Classroom's Koro-Sensei never planned to destroy the Earth, the whole premise of the show suddenly changes. Even if you hated a particular plot twist, it's hard to stop thinking about them once they've dropped.
While character death doesn't automatically constitute a plot twist, L's death in Death Note is definitely unexpected. Although Light Yagami had been attempting to kill L since the beginning of the series, few people expected him to succeed, and even fewer expected that he would do so 12 episodes prior to the end of the story. Even more surprising is that, as he lays dying, L expresses genuine emotional depth; that's a twist in its own right.
Fullmetal Alchemist: Brotherhood boasts a complex plot with plenty of twists, but one of the most alarming is the one about the philosopher's stone, a powerful magical item at the core of the story.
At first, the philosopher's stone is seen as the apex of the alchemist's craft; it can allegedly bypass the law of equivalent exchange, and basically produce anything its user desires. While the philosopher's stone is indeed quite powerful, its origin is horrifying. The stones are created through a fusion of souls from people who have been violently killed. One of the stones was created via the genocide of the Ishbalan people.
This nauseating revelation is made even worse by the fact that Roy Mustang — who claims that he wanted to protect the remaining Ishbalan people from further military abuse — uses this philosopher's stone to restore his own lost sight. While Mustang's morals were never perfect, this is still unexpected, given his character trajectory up until that point.
As far as the rest of the cast knows, Sōsuke Aizen of Bleach is a loyal member of Soul Society. He's a bit of a dork, and he likes to play by the rules. He's not the type of person one would expect to go rogue, as he's known for being dependable and kind.
Suddenly, he is mysteriously "murdered," and the blame falls on Ichigo and his friends. This is shocking enough on its own, but what happens next is one of the greatest plot twists in anime history; it is revealed that Aizen faked his own death in order to escape Soul Society, which he fully intends to destroy.
During the first part of Kill la Kill, protagonist Ryuko Matoi is dead-set on destroying the student council president Satsuki Kiryuin, who runs her school like a dictatorship. On top of that, she appears to be under the thumb of her mother Ragyo, who wants to destroy humanity using fibers from space. As Ryuko prepares to defeat her in an exaggerated battle, viewers are ready to see the prim president get clobbered.
As it turns out, Satsuki and Ryuko are actually on the same side. Satsuki has been slowly stockpiling her resources and honing her skills to stop her mother's evil plan, and now she needs Ryuko's help. Unbeknownst to her (or to the audience), Ryuko and Satsuki are actually sisters. Oh, and also Ryuko is a human/alien fusion. That's also a pretty big surprise, one that Ryuko takes so hard that she turns evil for an episode or two before agreeing to join forces with Satsuki.