The title says it all, I particularly like ch. 4&5 from :REverSAL so any manga (or book/media/whatever) similar to that would be good. To give a rundown for said chapters:

MC realizes the zombie-like characters aren't as monstrous as they seem. The "zombies" then get killed by new characters arriving on the scene but then, instead of just going with the flow and crying about it for 5 more chapters, the MC actually does something about it (in the form of turning her weapon on the new characters in order to protect the "zombies")