Practical_Day is one of the Days in The Days Union.
Practical_Day is traumatized by the war and does several experiments with dark creatures and diseases in the days basement. He considers himself the only sane day and has a theory that the dark creatures were made by the "Nights". He lives in a residence in The Days City.
After Albert gets invited to the Days house, Practical_Day takes him to the underground, and shows him several dark creatures. He also gives him a tour to a "Zoo" full of dead bodies and experiments. In the end, Practical_Day injects something into Albert, but never reveals what it is for.