day after day; every single day
Emphasizes the repetitive, unchanging nature of daily events, often with a sense of monotony or persistence.
来る日も来る日も雨が降り続いた。
It rained day after day without stopping.
彼は来る日も来る日も同じ仕事を繰り返
He repeats the same work day in and day out.
A fixed expression composed of 来る (くる, 'to come') + 日 (ひ, 'day') + も (also) repeated, literally 'the coming day and the coming day', emphasizing each successive day.