Sickness is a Visual Novel following the life of Suoh, a high school student turned violent criminal.
Orphaned, broke, and soon to be homeless, Suoh searches desperately for a way to provide for his twin sister, Sara. He starts to work long, physically-demanding hours, survives off instant food, and struggles to survive from one day to the next.
Just when things are starting to look bright, Suoh gets into a physical altercation with his boss. He blacks out, only to wake up moments later and find that his knuckles are bloody, his muscles ache, and there is a corpse at his feet.
But Suoh does not lament the loss of life. All he can think of is how badly he needed the money which his boss refused to pay him, and what he'll do next to get it.