Pastel World

Hart, Luther and Diaze live in a world that is connected to other worlds, dimention wise. Though the city (Niji city) is not suitable for other beings from different dimentions due to its... size, places like hospitals can use the ability to travel in and out of dimentions to cure other beings. The world consists of mainly cities and resorts, with short, pastel colored inhabitants with object heads. 

The goal of the Sanrio world and its hospitals is to bring peace and healing to the other dimentions. So big and small creatures would come through built-in portals, vortexes ect to get that kind of healing, from professionals in quantum to skilled surgeons.

The professionals are specially trained doctors, nurses and scientists who work with specialised weapons that specifically kill bacterias of any size, from the inside of creatures bigger than them to tiny little mice sized beings. 

Though it may sound like the dream hospital... There is an issue with that...

Despite being a good way of curing the (almost) incurable, bacteria or viruses may escape the patient. Those bacteria aren't small little things that destroy you from the inside, knowing they came from big patients from different dimensions, the bacteria are hell-a massive and can knock down buildings. Thus the signs "make this city better" as in "better fit" for such situations.