SETSUBUN — typically celebrated around February 3 — marks the end of winter; the day after the festival is when spring 'officially' begins. The tradition came to Japan via the Chinese sometime in the 8th century, along with Buddhism. Now, even though Japan observes the New Year on January 1 according to the Gregorian calendar, Setsubun retains shades of its previous significance as the Lunar new year. The traditions associated with are therefore, very much in the "out with the old, in with the new" mould.
It is believed that the time when winter changes to spring, or when the old year gives way to a new one, the worlds of living beings and the spirits are very close to each other. Thus, spirits — especially evil ones — and oni (demons) could easily cross over into the realm of humans, plaguing them for the rest of the year. To avoid such misfortune, a tradition known as "mamemaki" is observed.
For mamemaki, a family gathers fistfuls of roasted soybeans. The main door of the house is flung open and they pelt the soybeans out of it, to drive away any oni that are lingering by the threshold. At the same time, the family loudly chants: "Oni wa soto! Fuku wa uchi! (Devils out! Good fortune in!)". Sometimes, the head of the family or another male member of the household will wear an oni mask and pretend to be the demon at the door, disappearing when the soybean is thrown.
(If you're wondering why the soybean is the legume chosen, it is due to its stature as one of the five "most important crops" in Chinese lore. Soybean is believed to contain the spirits of all the cereals combined.)
Once the devils have been driven away, the family closes the door and settles down to a snack of roasted soybeans. Each person eats the number of beans that corresponds with their age, and an extra bean for luck. The main meal consists of "ehomaki" — an uncut makizushi roll that is made with seven fillings to represent the seven deities of good fortune. Strips of "gourd and cucumber, shiitake mushrooms, an omelette made with soup stock, eel, and denbu (mashed and seasoned fish; i.e. whitefish and shrimp that has been boiled, shredded, parched, seasoned, and coloured red)" form the customary ehomaki filling. Each member of the family must face the lucky direction for the year as decreed by the Chinese zodiac (2023's is reportedly the southeast) and eat the entire ehomaki in silence, while pondering over one's wishes for the new year. Lastly, the adults share a cup of sake and toast the advent of spring.
Some Setsubun traditions have changed over the years. For instance, there was initially a practice of burning dried sardine heads, whose strong smell was considered an anathema to evil spirits. Now, only a vestige of that custom remains, as some families cook/grill sardine for their Setsubun meal, while setting the head aside to make "hiiragi iwashi" — a talisman that is fixed to the outside of the front door. The sardine head is impaled on a twig along with some holly leaves for the hiiragi iwashi, which again, is said to repulse any inquisitive oni.
Setsubun celebrations have changed in another way. While it was previously celebrated at the household level, now it is far more common for people of one locality or neighbourhood to gather at a shrine or temple in the vicinity, where priests — and often celebrities, public figures and even sumo wrestlers — perform the mamemaki.