手紙に返事

reply to a letter

→ 手紙
phrase Rare #24,152
reply to a letter Usually followed by verbs such as する, 書く, or 出す. The に marks the letter as what the reply is directed to.
JA: 友達の手紙に返事を書きました。
EN: I wrote a reply to my friend's letter.

彼の手紙に返事するべきだろうか

Should I reply to his letter?

その手紙に返事を出す必要はない

You don't need to reply to that letter.

私の手紙に返事来なかった

I never received a reply to my letter.

会長個人的に私の手紙に返事くれるとは思いもよらなかった

I never imagined that the chairman would personally reply to my letter.