Hold up. All of the game's heroines got sick, leaving only Misaki to be the one to care for Hareta? This is 100% the world starting to change, including Misaki as a secret heroine of sorts, or Misaki is becoming the actual protagonist.
If it's the first one, then there's one conclusion possible: the world has ALREADY changed. Hareta was not given an option here. Hareta is ALREADY on the impossible Misaki route.
VNs (Dating Sims in particular) usually have this thing that, when a route is selected, the player stops getting important choices involving the other heroines and is basically just there for the ride. Could this be that?