Salut, hola, and howdy! This looks super promising, and I am a bit of a sucker for cyberpunk, so I'd love to join. I do know that you intend the cast to be the bums of this world, and I certainly don't want to dance outside your vision, so I figured I'd ask if any of my first ideas are cool with you!

My first idea was a former employee of a privatized security firm, eventually parting ways (probably for health-related reasons or the like), who then faced a system that is as cruel as it is dismissive. 

Another idea would be the devout follower of a small-time gang leader, who disappeared, leaving the character in question behind with no real direction or sense of purpose. They could simply try and uphold daily operation in hopes of their admired boss returning, or perhaps put themselves in a poor position out of distress.

I also thought up a small-time cult/gang leader, who was percecuted after coming across as a little too ambitious, and then had to flee into the underworld as to escape the clutches of those who saw a potential threat in him/her.

My last idea is an A.I., or perhaps an usually heavily modified human, who served as a sort of experiment, then got discarded, but somehow escaped the intended destruction/murder, and found themselves forced to live the lowest possible life, as they'd not just be an outcast in the normal world, but would find themselves endangered.

Edit: Actual last idea: A journalist who teetered around the acceptable borders of "free press". After one too many reports that painted the mighty CEOs in an unfavorable light, they had to escape from an assassination and promptly found themselves forced to leave their old life behind, and start over in the underworld.

So yeah, if any of those works for you, I'd be happy to flesh it all out.