Intro. So you've been displaced as a bacteria, you've been surviving off scraps. Then you somehow flew up into a large black mass with other monstrous bacteria.
You survived the onslaught that insuded when you awoke, being a human you've used your brain. You found a dead cell, and removed their clothes.
You've now been living among the cells, as the body's one and only multi cellular/parasitic/bacteria/ that also does many different jobs. You help platelets/red and white blood cells/T cells and much more.
You live in a former dead cell, that you brought back to life. Making you the first zombie cell, not quite zombie but the place you live now is like a haunted house to passersby. Zombie to the eyes above, or in the macro world.
Currently the body of your host is a teenager, who constantly almost dies all the time. You lived in ruins, now your middle class now. And your not going to let this body die by any means, time to get to work!