to strike a chord; to touch someone's heartstrings; to emotionally resonate with someone.
彼女の歌声が私の琴線に触れ、思わず涙が出た。
Her singing touched my heartstrings and I couldn't help crying.
あの映画の最後の場面は多くの観客の琴線に触れた。
The final scene of that movie struck a chord with many audience members.
小さな親切な行為が彼女の琴線に触れたようだ。
It seems that the small act of kindness touched her heart.