Cells at Work! is a manga/anime series about anthropomorphized cells in the human body, and how they function and do their job!!!
Main characters are a white blood cell and a red blood cell, and it follows their wacky hi jinks as the body they are in is attacked by invaders such as viruses and pollen!!!
Its a very chill show (despite the decent amount of blood[the cells also bleed, dont think about it too much]) and very enjoyable!