肝かん胆たん相あい照てらす

expression, godan verb (-su)

be profoundly compatible; be inseparable; open one's heart to each other

Idiomatic expression describing a relationship of deep mutual trust and understanding, where each person reveals their innermost thoughts and feelings. Often used in formal or literary contexts.

• 彼かれらは肝かん胆たん相あい照てらす仲なかだ。

  They are so close that they open their hearts to each other.

• 長なが年ねんの友ゆう情じょうで、二人ふたりは肝かん胆たん相あい照てらす関かん係けいになった。

  Through years of friendship, the two developed a relationship of profound mutual understanding.