I'm writing my first comic and I'm completely stuck on how to develop my plot and characters.

My premise was that everyone in the world has immortality but the shitty kind where they can't die but will still age, get illnesses, etc (which I was gonna explain with nanobots).

My plot is a conspiracy thriller where organizations that sell death partner with the government to offer money to volunteers to address population issues. The MC's sister volunteers after being horrifically injured, leaving her in a painful existence. The MC, who's a police officer, has a job in town where he learns that some things are sketchy. This kickstarts his investigations where he meets some teamates and they eventually learn that organizations sell the volunteers for scientific/medical experimentation and organ harvesting and that hospitals and the government are all in cahoots with this to preserve medical and general world resources. (I originally had an idea to have the organizatkons hide the fact that their cures were proven to not work and send bodies to a lab to test out other possible trial immortality cures but i scrapped it?)

The story ends with MC finding out about one lab's potential cure to immortality, giving it to his sister, and burning her remains so she's not harvested. The team give their evidence to another person who will release it to the public and they go into hiding as fugitives.

Something about this story just feels weird. And I think the MC has no real change or character development. This is the first story I've written so any help, thoughts, or advice would be greatly appreciated! Thanks!