Traitors in anime have been responsible for increasing the stakes with their actions. The actions of the traitors bring about unexpected plot twists and depending on which side they betray, these traitors can either earn the love or the hatred of the fans.
The characters who betray the good side are more common as their actions leave the protagonists in peril, thus making the story more interesting. These traitors do get taken down in the future, but there are some characters who actually managed to make amends for their actions. With that in mind, here are some anime traitors who were able to redeem themselves.
6 Hendrickson (Seven Deadly Sins)
Hendrickson made his debut in the very first season of Seven Deadly Sins. He was a Great Holy Knight, who conspired with Dreyfus to take down Zaratras and then pinned the murder on the Seven Deadly Sins, which caused the group to be branded as traitors. When he unlocked his demonic form, Hendrickson was easily able to overwhelm the Seven Deadly Sins and the other Holy Knights.
He was so ruthless that he didn't even hesitate to attack and kill Hawk. However, after he was defeated by Meliodas, Hendrickson completely changed his ways and tried his best to make up for the damage he had caused to everyone. Later on in the series, he even offered his body to one of the Archangels so that he could take down members of the Demon Clan.
5 Itachi Uchiha (Naruto)
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He is one of the most famous anime characters of all time. Originally, Itachi was introduced as a villain, who massacred his entire clan, including his parents. He didn't stop there, and after his younger brother came back home, Itachi used genjutsu to make Sasuke experience the killing of their parents. This left Sasuke emotionally scarred and traumatized him for life.
As the series moved forward, it was revealed that Itachi was forced to kill his clan members by Danzo. Also, by defecting from the Hidden Leaf and joining Akatsuki, he was actually trying to protect the Hidden Leaf from the shadows. Furthermore, after being reanimated during the Fourth Great Ninja War, Itachi stopped Kabuto and brought an end to the reanimated army of ninjas who were causing widespread destruction.
4 Reiner Braun (Attack on Titan)
Reiner is among the best characters in Attack on Titan. He was revealed to be the Armored Titan, who destroyed the walls and caused many casualties. His betrayal wasn't normal. Reiner had been a member of the Survey Corps for so long that he started to believe that he was born on Paradis Island.
The confusion in his mind often caused him trouble. Reiner might not be a nice guy, but what he did was for the sake of his own family. He is not a mass murderer like Eren Jeager, who wiped out more than half of the world's population. Reiner's character development especially in the fourth season of Attack on Titan redeemed him, and it is fair to say, that the more the fans saw of Reiner, the more likable he became.
3 Askeladd (Vinland Saga)
Askeladd was introduced early on in Vinland Saga. He was a mercenary leader, who would get the job done at all costs. He was responsible for the death of Thors, who was considered a legendary warrior. Askeladd did not hesitate to use Thorfinn to make Thors surrender and then ordered his men to kill him. His attitude made him a detestable character.
Askeladd betrayed his own men and their trust, and he openly said that he hated all of them. After openly announcing his hatred, Askeladd even killed many of his men. His redemption came towards the end of the first season when he lobbed off the head of King Sweyn and helped Prince Canute to come to power.
2 Sasuke Uchiha (Naruto)
Sasuke Uchiha is Naruto's best friend and rival. He was traumatized at a very young age by Itachi, who used a high-level genjutsu on him. Most of Sasuke's life was spent hating Itachi and gaining more power and once he found out the truth about Itachi, Sasuke's entire world came crashing down. He decided to make the world pay for their actions starting with the Hidden Leaf. Sasuke attacked Danzo and killed him.
He also attacked the Fourth Raikage, which led to him being branded an international criminal. Sasuke did redeem himself during the Fourth Great Ninja War by helping the Shinobi Alliance to defeat Obito, Madara, and then Kaguya. He also exiled himself from the Hidden Leaf and traveled the world to ensure that there were no threats remaining.
1 Nami (One Piece)
Nami is a member of the Straw Hats and she is their navigator, which makes her one of the most important members of the crew. She met Luffy in Orange Town for the first time, and then she stayed with the crew until the Baratie Arc. However, after the arc ended, Nami left the crew and took the Going Merry with her. This left Luffy and co. speechless as they didn't expect Nami to do such a thing, but as they followed her, they found out that Nami went back to her village to free it from Arlong's tyranny.
So, she did not do such a thing out of her own free will, but because she wanted to help her sister and the rest of the villagers. While it might not be a major betrayal, she did break the trust of her crewmates, however, she made up for it by rejoining the crew and helping them to navigate through the seas safely.