expression, godan verb (-u)
get along well; be in sync; work well together
Describes people whose timing, feelings, or actions naturally match, often in teamwork, conversation, or performance. Literally 'breaths match'.
彼とは呼吸が合うので、一緒に仕事がしやすい。
He and I are on the same wavelength, so it's easy to work together.
デュエットで呼吸が合わないと、いい演奏にならない。
If you're not in sync in a duet, it won't be a good performance.