do ... to each other, do ... together
私は彼女と訪問し合う仲だ。
She and I visit each other.
それは核ミサイルをボタン一つで操作し合う戦争になるだろう。
It would be a war in which nuclear missiles are launched at each other with the push of a button.
協力し合うこと
Cooperating with each other
— 君の名は。 (2016)
私は彼とは訪問し合う仲だ。
He and I visit each other.