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The backgrounds of many powered individuals due to the trauma necessary for you to have a trigger event.
The Undersiders have been through so much.
Bitch was abandoned by her mom, and shuffled around from foster home to foster home because she simply wasnít good looking enough for others to want to adopt her. Unable to socialize, her only friend was a stray dog that she took care of and who was trapped in a pool drown by a foster mom to punish her for not obeying her. Her trigger event caused her pet to go wild and massacre her foster mother and siblings. She has been on the streets ever since and her power has actually made it almost impossible to connect with people. In her interlude, she privately wishes she could be closer with the rest of her team, but knows she will never belong. It says something that her screwed up relationship with Taylor is the best human relationship she has ever had.
Alec was raised by Heartbreaker, who punished and tested him with terrible emotions growing up. After one such occasion, he didnít speak for months. Growing up he had no close family due to being neglected by his fatherís victims. After his trigger event, he was pushed to kill and torture people so his father could still find a way to control him. After finally killing someone, he ran away. But he is effectively a sociopath now. He doesnít feel any remorse for the things he did for his dad, only that he felt it was pointless.
Worse? On some level, he's aware that there's something very wrong with him, but he's so emotionally dead inside he can't work up enough passion to be unhappy about it. The closest thing he has are the emotions of people he's puppeteering sent back through the link.
Taylor's mom is dead, and her best friend betrayed her and joined a group of bullies. She has to go through sheer hell everyday. She was locked in a locker stuffed with used tampons, and despite everyone seeing it happen, no one got a teacher or tried to help her. She actually began to have a panic attack as hours went by and no one came to help her. It caused her trigger event, and the resulting senses from the bugs nearly caused her to have a mental breakdown and she was actually hospitalized. Despite all of this, no teacher would help, one of the bullies lawyer father got them off, and things just kept getting worse and escalating. Things have just gotten worse and worse for her throughout the story, and she feels extreme guilt at the things she has done. She has outright stated that she doesnít think she deserves to be happy.
Brianís mother is crazy and neglectful and he was raised by his very hard father. He was forced to train and spar in the gym against him, and his father didnít hold back. He wants to take custody of his sister to get her away from his mother but privately worries that he wonít be able to help her. He also laments that he has very few social skills and close relationships due to his upbringing and lifestyle.
Aisha is a serial runaway who was raised by her mentally imbalanced mother and it is strongly implied that she was abused in some way by one of her Mother's boyfriends. Aisha has very few social skills and feels terrible about what Brian is suffering through after the 9. She wants to help him, but she simply doesn't know how.
A particularly vivid illustration of her life before she joined the Undersiders comes at the beginning of Interlude 13-1/2, when she visits her mom while hiding behind her Perception Filter.
Tattletale's older brother committed suicide for reasons no one could figure out. She mentioned to her family that she had noticed him acting different before he died, and in their grief, they blamed her, calling her stupid for not noticing and saying something about it earlier. She had her trigger event after spending night after night agonizing over how she should have figured out what was going on with him and told someone. When she finally got her powers, she could see how everyone was acting fake after her brother's death, especially her father, who realized that she had powers and started pretending to be affectionate towards her in order to get her to use her powers for his benefit, at which point she ran away from home. It also turns out that the reason Tattletale has always gone out of her way to help Skitter/Taylor from the very beginning is that she could see immediately that Taylor was trapped in the same state of hopeless despair that her brother was, and feels driven to save her because she couldn't save her brother.
In Extermination 8.8, Taylor is visiting the monument to the capes who died fighting Leviathan, and, at the bottom of the list, sees where Bitch carved the misspelled names of the dogs she lost.
What we learn about Battery's fate is awful on multiple levels — she has always felt extreme guilt about getting her power from the obviously-shady Cauldron and agreeing to do three favors for them on pain of being stripped of her power or worse, so when she is told to let Siberian and Shatterbird escape, she plans to do what is right and kill them when she has the chance ... but she is poisoned by Bonesaw's spiders before she has a chance. She dies slowly and painfully in a hospital bed, delirious, as she begs for Legend to affirm that she tried to do the right thing.
Using Kid Win's adaptation of Armsmaster's lie detector, Legend confirms that not only the staff of Cauldron, but Eidolon and Alexandria (his two oldest comrades), have been lying to him. They have been experimenting on humans. They have been letting superpowered serial killers escape. And are all conspiring to at least enable the end of the world.
In Monarch 16.7, during the conversation after Taylor goes to meet her dad, Danny, for lunch and finds he has his friends over:
Kurt [chuckling]: I'd offer you a drink, but that'd be against the law. How old are you, anyways? Taylor: Fifteen. Danny: Sixteen. [Taylor turns to look at her dad] Danny: It's the nineteenth. Your birthday was a week ago. Taylor [remembering she was fighting the Slaughterhouse Nine then]: Oh. Kurt: That's the saddest goddamn thing I ever heard.
Chrysalis 20.5, after Taylor escapes from Dragon and Defiant's ambush — an ambush which outed her in front of half the high school students of the city — she heads home, only to find her father surrounded by PRT officers with his head in his hands as if he's just heard some very bad news. She sends a single butterfly to him, because she doesn't want what might be her last contact with him to be ugly.
Imago 21.2: Taylor visiting her mom's grave for the first time since the story started, and trying to tell her what happened.
Taylor: I guess things have kind of turned upside down. That whole superhero thing I told you about, before? It... really didn't work out.
Imago 21.4, Skitter and Grue lie together for one last time when they realize that they don't have a future together.
After her visit to Tattletale in Imago 21.7, when we discover what she had been doing ever since she visited her mother's grave:
We'd established something of a rule, way back when, on the night we'd first found out about Dinah and her powers, the same night Leviathan had arrived. I'd very nearly turned my back on the group, and Tattletale had established a rule.
After Tailor leaves the Undersiders Bitch is in denial, convinced it is some kind of ruse. When she publicly announces her intent to become a hero, removing all doubt, we hear all the dogs in Brockton Bay begin to howl, responding to Bitch's grief.
In 24.4, Regent's Heroic Sacrifice to draw Behemoth's attention away from Imp. Greater love hath no man than this.
wash17: After finishing this chapter. I sat for a minute. I then got up, and got out an old bottle of scotch. I poured two glasses, and walked out into the damp mourning. I looked up at the stars, and poured a glass out for regent. I raised the other to capes lost in this battle, the fights of the past, and for what is to come. Godspeed.
What some consider even more tragic than his death is that he didn't get to finish whatever snarky one-liner he was building to before getting zapped.
In Interlude 24 we see the first Wards team, and see what the program was originally about-giving young capes a chance to be safe and be kids. As Chevalier sadly notes, the program has departed a lot from its original roots. Worse, of those kids, at least half of them are dead by the present day-horribly so, in the case of Mouse Protector.
From Interlude 26 (Donation Bonus #1), Defiant's reaction to Dragon's death. Saint dismissal of his feelings as "fetishes and self-delusions" just makes it worse.
Theo's thoughts at the beginning of 26a. Bet you never thought you'd be sad about Empire Eighty-Eight.
The reason Scion looks so sad? He's actually one of the twin power-granting entities, and his counterpart has died. His species is on the brink of extinction and his only purpose in life, however destructive, has vanished.
The devastation caused by Scion's rampage is incredibly bleak, especially Taylor's reaction to her father's death: she flies up into the air and lets her flight pack expend its charge, which would have resulted in a fatal fall if not for Tattletale.
Taylor reflecting on all the sacrifices she's made, of herself and of other people, in order to stop The End of the World as We Know It, and realizing that it was all for nothing. The resulting suicide attempt just makes it worse.
Speck 30.1, Taylor's inner monologue, leading up to her thinking: "Goodbye, Undersiders."
Speck 30.2: Taylor realizing that not only can she no longer talk, or interact with another human within sixteen feet without controlling them, her brain is so damaged that she can no longer understand written language and can't read.
The ending of Speck 30.7 and Worm's main story: Contessa seemingly kills Taylor following her saving humanity and the multiverse from Scion, but it turns out that she was merely depowered and taken to Earth Aleph with her father.
The reveal in the final epilogue that Grue didn't survive the fight on the oil rig, and that Tattletale lied to Taylor so that she wouldn't have to deal with another loss before the fight was over.