festive New Year's mood
Refers to the cheerful, relaxed atmosphere associated with the New Year holiday, often implying a slight tipsiness from drinking toso (spiced sake).
At the New Year's gathering, everyone seemed to be enjoying themselves in a festive New Year's mood.
Compound of 屠蘇 (toso, spiced sake drunk at New Year) and 気分 (kibun, mood, feeling). The exact origin of the phrase is uncertain, but it evokes the warm, convivial feeling of the New Year holiday.