one-sided correspondence; writing without receiving a reply
Describes a situation where one writes letters or messages but gets no response. Often carries a sense of loneliness or neglect.
I sent him many letters, but it turned into one-sided correspondence.
When one-sided correspondence continues, I gradually lose the motivation to write.
Compound of 片 (kata, 'one side') and 便り (tayori, 'correspondence, news'). The exact historical derivation is uncertain, but the meaning is transparent from its components.