Setsubun

In volume 34 of Ranma ½ (Japanese or Fanscan version) the first story arc is on Setsubun.

Setsubun is the day before the first day of each season. Though most of the time when you hear Setsubun they are talking about the day before the first day of spring (last day of winter). The date is either the 3rd or 4th day of February. The day is determined by the old lunar calender.

On the evening of this day a bean throwing ceremony (mamemaki) is held at homes, shrines, and temples. Bean throwing ceremony consists of scattering roasted soybeans while chanting Oni wa soto, fuku wa uchi (Out with the bad luck, in with the good). Often someone usually the father will wear an oni mask and be chased around by children throwing beans at him. The point of the ceremony is to bring good fortune and drive out evil spirits.

Additional traditional things done on this day include the eating of one bean for each year of your age, celebrities throwing beans at the crowds during festivals/shrines, and some people hang a Japanese twig (hiiragi) together with the head of a sardine at the entrances to their homes to shut out evil spirits.