One can learn a lot about an anime character by studying how they respond to deeply traumatic situations. In addition to adding drama, alarming plot lines can expose viewers to aspects of their favorite characters that aren't usually on display. By paying close attention, one can gain valuable insight into who a character is, and why they behave they way that they do.
In A Silent Voice, a young girl is bullied for being deaf, leaving everyone involved traumatized. Meanwhile, in Tokyo Ghoul, Ken Kaneki's personality completely changes after he experiences torture at the hands of a man-eating monster. Some characters' responses to trauma accurately depict real-world PTSD, whereas others' reactions feel imagined and unbelievable.
For someone with such a terrifying backstory, Edward Elric of Fullmetal Alchemist: Brotherhood is remarkably emotionally stable. When Edward was a little boy, his mother died of an unspecified illness. Desperate with grief, he begins studying alchemy, and attempts to raise his mother from the dead. Unfortunately, rather than reviving his late mother, Edward only succeeds in creating an undead monster. Additionally, the gamble costs him two of his limbs, and destroys his brother Alphonse's body completely.
After recovering from the terrifying event, Edward and Alphonse make it their mission to restore their bodies. They work tirelessly to achieve this goal, but end up embroiled in far greater issues. After experiencing great trauma, Edward develops a noble desire to protect others from suffering.
Ken Kaneki has been through a lot. In Tokyo Ghoul, the hero is subject to a not-so-great home life, and winds up being brutally attacked by a man-eating ghoul whose organs fuse with his own to create a ghoul/human hyrid that needs to consume human flesh to survive. That all sounds pretty rough, yet Ken doesn't actually react that strongly to the horror. Instead, he represses most of his actual emotions (after an initial freakout), and convinces himself that his circumstances are acceptable.
Ken's demeanor changes dramatically after he's tortured by a ghoul named Yakumo Oomori. Oomori employs a variety of inventive torture methods, such as repeatedly cutting off Kaneki's fingers and forcing them to regenerate, or putting a Chinese red centipede in his ear. The experience leaves Kaneki so physically and psychologically broken that his old defense mechanisms no longer work. As a result, his personality hardens dramatically, and he becomes capable of hurting others for his own personal benefit.
Guts of Berserk has arguably one of the worst childhoods in anime history; any one of the horrible things that's happened to him would completely wreck a normal person. As a newborn, Guts was found beneath his mother's hanged body. From there, he's adopted by a mercenary named Gambino who regularly beats him, and eventually begins advertising the young Guts's services as a sex worker. Later, Guts survives a terrifying supernatural event called the Eclipse that leaves him severely injured and branded with a mark that attracts dangerous supernatural forces.
How does Guts deal with this his life of trauma? He becomes a miserable, hard-hearted man who will stop at nothing to achieve revenge. As a side-effect of this, Guts regularly finds himself acting violently towards his loved ones, despite his best efforts to remain calm. Guts is deeply scarred by his past, but considering how the world of Berserk regularly features religious zealots being burned at the stake, there probably aren't too many qualified therapists hanging around.
Just about everyone in Attack on Titan is traumatized to some degree, but Eren Jaeger is arguably the most vocal about his issues. After being confined in a small, crowded town (so as to avoid being eaten by giant, humanoid monsters called Titans), Eren is fed up with his life, and ready to fight for his freedom. That desire increases exponentially when his town is attacked, his home destroyed, and his mother is eaten in front of his eyes.
After escaping as a refugee, Eren joins the Survey Corps to help destroy the Titans. Even after he gains power, Eren still has nightmares and flashbacks related to his skirmishes with the monsters, and his rage increases exponentially with each new battle.