Many characters have suffered at some point in their lives, some worse than others. A single event can be enough to completely warp a character's personality or their sense of what is right or wrong. Despite how tragic their pasts may be, the things that they have done can't be excused so easily.
Although some of these characters are aware of the fact that their actions are not right, they justify their actions by their experiences rather than stop themselves from doing the wrong thing. Sometimes it is easy to understand where these characters are coming from, but one action does not always excuse another.
10 Akame Ga Kill: Seryu's Father Was Killed, So She Has A Warped Sense Of Justice
Seryu's Father was part of the Imperial police but was killed by people who opposed the Empire. His teachings to Seryu about the importance of justice became warped. Although the Empire was indeed corrupt, she assumed that anyone who dared to oppose it was evil and deserved to be destroyed.
She became more deranged when her Captain was killed, and she was responsible for some deaths that she took great pleasure in.
9 Code Geass: Lelouch Had To Raise His Sister After His Father Turned His Back On Them
When his mother was assassinated, Lelouch's sister Nunnally survived, but was paralyzed and blind as a result. They were both outcasts after Lelouch confronted his father about his mother's death, and were forced to move to Japan.
He eventually decided that he wanted to overthrow the corrupt government after gaining the power of the Geass, as he wanted to create a peaceful world in which his sister could live. However, he was responsible for killing and manipulating people in order to achieve that goal.
8 Dragon Ball Z: Vegeta's Planet Was Destroyed
Vegeta was a hostage who was forced to commit unspeakable acts for Frieza. Despite doing as he was told, Frieza wiped out most of the Saiyan race as well as the planet. Despite this, Vegeta had to continue working for him, knowing that Frieza was stronger than he was.
Although Frieza shaped him into a killing machine, Vegeta himself wasn't blameless for all of the deaths that he had caused and even enjoyed.
7 Elfen Lied: Lucy Was Bullied Until She Snapped
Thanks to her unique appearance of pink hair and white horns on her head, she was bullied by other children. They would perform outrageously cruel acts that no children their age would realistically do.
Lucy eventually got attached to a puppy, but the bullies ruthlessly took advantage of that. This made Lucy snap, killing every person who had ever treated her poorly. At that point, she found it justified to kill anyone who betrayed her, going so far as to kill her best friend's family because he told her a small lie.
6 Fairy Tail: Ultear Milkovich Was Experimented On & Assumed Her Mother Replaced Her
Ultear was taken from her mother, Ur, who was told that her daughter had died. Ultear was then subjected to a variety of painful experiments in order to give her powerful magic. She managed to escape from the facility but saw her mother happy with her new apprentices.
Feeling betrayed, she went back to the facility. She served as an antagonist for a large portion of the series, manipulating Jellal and even trying to trick Gray Fullbuster into sacrificing himself.
5 The Promised Neverland: Isabella Raised & Sent Children To Their Deaths In An Attempt To Survive
Isabella is a Mother, a person who cares for and raises the children at Grace Field House. Her real job is to keep any of the children from escaping. When they reach a certain age, she sends them off to be eaten by Demons.
It is revealed that she had a similar upbringing to the children, and chose to become a Mother in order to survive, which was her way of spiting the Demons. However, the Demons proved that they were willing to kill anyone at any time, and she was never truly safe.
4 Seven Deadly Sins: Gloxinia Joined The Demon Army After He Assumed His Sister Was Killed
Gloxinia was the former fairy king, who trusted humans to watch after the forest and his sister while he went off to fight the Demon Army. When he returned, he found his sister brutally injured and in the arms of a human.
Immediately blaming the human and writing his sister off as dead, he killed him and would go on to kill many others after joining the Demon Army. His sister survived, and Gloxinia realized his actions were not justified at all after meeting King.
3 Food Wars: Azami Nakiri Wanted To Help His Wife
After Azami married Mana Nakiri, she fell ill, unable to eat anything due to having the God Tongue. Deciding that the culinary world was to blame, Azami wanted to change it.
He started with training his daughter, isolating her from the outside world and forcing her to compare dishes, throwing away whatever he deemed worthless. Years later, he took over Totsuki Academy and planned to assimilate the students as well as the restaurants in the world to cook the way he wanted them to.
2 Assassination Classroom: Gakuho Asano Wanted To Raise Strong Students
Gakuho was originally a teacher similar to Korosensei. He had a close bond with his students, and he did an excellent job of teaching them. However, once one of his students took his own life after being bullied, Gakuho decided to raise strong students instead of kind ones, so nothing like that would happen again.
As a result, he manipulated the bullies into becoming gambling addicts and created a new school in which students would look down on the lowest class, struggling to maintain good grades in order to avoid being ostracized as well.
1 My Hero Academia: Shigaraki Tomura Had A Terrible Father
Shigaraki's father was bitter about the fact that his mother, All Might's former mentor, had abandoned him. Despite the fact that she did it to keep him safe, he was never able to forgive her for leaving him behind. As a result, he would often abuse Shigaraki for even mentioning heroes while the rest of the family did nothing to intervene.
This led to the activation of his decay Quirk, which took the lives of his entire family. From this point on, he would kill many more people with his Quirk.