noun
menstrual period days
Euphemistic wasei-eigo from English 'blue day', referring to the days of menstruation. Often used in feminine product contexts or casual conversation.
wasei-eigo (Japanese-coined English), from blue day
ブルーデーには体調が優れないことが多い。
I often feel unwell during my period.
ブルーデー用のナプキンを買いに行く。
I go to buy sanitary pads for my period.