The Common Cold (Manga)

A Normal Cell who is bored of his monotonous duties and annoyed by his rowdy Killer T Cell neighbors is befriended by a mysterious cell who doesn't speak and wears a strange hat. The two have fun pulling pranks on various cells. Eventually, the stranger reveals himself to be a cell infected by a virus, with his hat being the replicating virus. He attempts to infect the Normal Cell, but the immune cells arrive in time to wipe out the virus. After identifying the virus as Rhinovirus (The Common Cold), the immune cells lecture the Normal Cell to study so that he can identify pathogens in the future.