His time in the war as a young man has continued to haunt him throughout his life. The things he's seen, the things he's done all come back in flashes of memory that put him right back in that place. Aaron wants to take those horrors and his guilt and turn it into something that makes life better, not just for him, but for those he cares about.
Frida has lived on the streets for the last couple of years, after her parents neurine addiction really took hold. They spent more time in a neuroscape than raising her, and she doubts they've taken much notice of her being gone. She knows she has other family out there, but, for now, she's accepted her found family and they watch out for her.
The world has taken a bad turn, but Gary has been around long enough to know these things run in cycles. This may be the worst, but that doesn't mean it is unfixable. He's set out to do it and has brought this motley crew together to help. He needs them and they need him. Despite their differences, they complement each other well.
Too young to have been in the war, Lena took up medical training at a time Pacifica desperately needed doctors. She excelled at school, but with it came a drug addiction, starting with uppers and evolving into neurine. This made it hard to keep a job at a hospital, and she didn't like the kinds of people who could afford healthcare anyway. Now she works as a medic to those who pay her what they can afford.
It's a scary place out there, so why would you ever leave the house? Sammy has chosen not to. Their friends don't know what Sammy looks like or even where their human body is. Sammy would prefer to keep it that way and would also like to find a way to leave their body behind altogether.