From Google Translate:

Momoya Togawa works as an elementary school teacher in a certain town in Chiba Prefecture in 2018. A good, “ordinary” father who takes care of his family.

He was enjoying small but warm moments of happiness, such as celebrating the discharge of his eldest son, Aio, from the hospital with his wife, Koharu, at their new home. But one day, a postcard is delivered to him. That picture postcard transforms his "ordinary" daily life into something disturbing... A father confronts his “coinciding fate” guided by a picture postcard! The story of confronting the coincidence of fate'' drawn by the author of The Town Where Only I'm Missing'' begins! !