adverb
reluctantly; against one's will; despite oneself
Used when someone does something they would rather not do, often out of obligation or necessity. Conveys a sense of unwillingness or lack of enthusiasm.
不本意ながら、その提案を受け入れた。
Reluctantly, I accepted the proposal.
不本意ながら、彼は転勤を命じられた。
Against his will, he was ordered to transfer.
いやいや is more casual and direct about doing something unwillingly, often used in speech.
From 不本意 (unwilling, reluctant) + ながら (while, although). The combination forms a set adverbial phrase meaning 'although unwillingly' or 'reluctantly'.