Betrayal is a common theme in anime. It's a good way to trick or shock the audience. Aizen's betrayal of the Soul Society in Bleach is one of the more famous instances of betrayal. His betrayal of his comrades is extreme as he tricked them for years then attempted to kill several of his comrades when the truth finally came out.
Most of the time, betrayal isn't just somethings villains do. Both heroes and villains can deceive the people close to them and mostly, they feel that the betrayal is justified. Usually, a character will turn on their friends or comrades, but there are a few anime characters who have even betrayed their families.
10 Shou Tucker Was A Monster (Fullmetal Alchemist/Fullmetal Alchemist Brotherhood)
Most anime fans are very familiar with the betrayal Shou Tucker committed in Fullmetal Alchemist. He initially appeared as a loving father and a brilliant scientist, famous for creating a talking Chimera. The rose-tinted glasses eventually fell away to reveal the monster Shou Tucker really was. He became completely obsessed with his research. Not only did he kill his wife by turning her into a Chimera, but he performed completely unethical experiments on his daughter and the family dog. Tucker is one of the most hated characters in anime because of what he did.
9 Itachi Uchiha Destroyed His Clan (Naruto)
Itachi Uchiha is also famous for his betrayal in Naruto. He abandoned his family to become a rogue Shinobi. He killed all the members of his clan, including his parents. The only one who survived the massacre was his younger brother Sasuke. Itachi may have had a justified reason for killing his whole family, but it was still a betrayal nonetheless. Understandably, Sasuke despised him and grew to despise the village that made Itachi betray his family.
8 All For One Tried To Control His Brother (My Hero Academia)
All For One was seemingly born evil. It's hard to say he betrayed anyone when it was expected of him. However, All For One was most likely a normal man at some point until the thirst for power consumed him.
In My Hero Academia, he eventually became a tyrant - willing to stop anyone who got in his way, including his own brother. One For All locked his brother away then forced a Quirk on him in order to make him submit. His brother resisted and forced the Quirk on him, creating the only Quirk that could beat him, One for All.
7 Ren Sohma Abused Her Daughter (Fruits Basket)
Ren Sohma is a character whose betrayal is a little harder to spot. She was manipulative and hateful towards her daughter Akito, which in turn created Akito's own manipulative behavior. Ren thought that she deserved special treatment because she was the mother of the Zodiac's God. Since she wasn't treated like a God herself, she became resentful of Akito and treated her terribly. She even tasked Isuzu with stealing from Akito. Rather than one moment of betrayal in Fruits Basket, she spent all of Akito's life betraying her.
6 Tamaki Suoh Went Against His Family's Plan (Ouran High School Host Club)
Tamaki Suoh was an airheaded and happy-go-lucky person who didn't seem capable of betraying anyone. When he's engaged to a woman, he not sure himself if he's willing to go through with it to make his family happy. Especially his grandmother who seemed to hate Tomaki just for existing. Thanks to Haruhi's interference Tomaki went against his family's wishes and rejected the engagement. It's a pretty mild betrayal but a betrayal, nonetheless.
5 Satsuki Kiryuin Stabbed Her Mother In The Back (Kill La Kill)
Satsuki is a complex character, initially seeming cold but able to open up and relate to others over time. Her relationship with her mother was complicated - she was treated more like a tool than a daughter. Ragyō treated Satsuki so poorly that Satsuki had plans to secretly rebel.
Her mother experimented on her by exposing her to Life Fibers. Kill La Kill also showed that her mother sexually abused her. It's no wonder Satsuki eventually betrayed Ragyō by literally stabbing her in the back.
4 Light Yagami Lied To His Family (Death Note)
To his family, Light was an intelligent and loving person. He always got good grades and stayed out of trouble. Unbeknownst to them, Light was consumed with killing criminals and becoming a god. The Death Note allowed Light to kill anyone whose name was written down, all he needed to know was their name and what they looked like. With that power, Light killed hundreds of people. He constantly lied to his father about what he was doing. In Death Note, his father heavily suspected him of being the killer. It's almost lucky that his father never lived to see the truth come out.
3 Hiruzen Sarutobi Betrayed The 4th Hokage's Trust (Naruto)
Hiruzen Sarutobi was the 3rd Hokage and was considered a great man for a long time. He was Hokage for the longest and because of that, the entire village looked up to him. As more of the past was revealed, people began to realize that he wasn't a good Hokage.
When Naruto's father (the 4th Hokage) died, he wanted Naruto to be treated like a hero for becoming a Jinchuriki. Instead, Sarutobi allowed the entire village to despise him and sat back as Naruto became an outcast. In Naruto, the complete betrayal of the 4th Hokage's trust probably had the man rolling in his grave.
2 Ray Sided With His Friends (The Promised Neverland)
The Promised Neverland's Ray was a double, or even triple, agent. He was initially acting as a spy for his mother, but eventually revealed he was never on her side. Once he gained the other children's trust, he started to distract his mother while the rest of the kids figured out a plan of escape. Unfortunately for him, his mother became wise to his betrayal and managed to trick him in return.
1 Zuko Betrayed His Family For The World (Avatar: The Last Airbender)
Zuko was one of the few characters who had good reason to betray his family. He was the son of the Firelord, who was trying to take over the world. Although Zuko sided with his nation at first, he eventually realized he was on the wrong side of history. In Avatar: The Last Airbender, he became a complete outcast and was even more hated by his father for betraying him. Luckily for Zuko, it worked out well for him in the end.