Bonenkai are a December tradition in Japan.
忘年会/bonenkai mixes the characters for “forget”, “year” and “gathering” together.
It’s an annual drinking party held by work, friends and other social groups.
You drink together and forget the woes of the past year.
They’re held at izakayas which serve food and drinks.
Many people have several different bonenkai to go to which leads to a lot of hungover workers in December.