From the article:

The novel will follow four different stories including: a rare card Ichikawa Kyotaro received as an elementary school student and the mysterious woman he met at the time, Ichikawa and Anna Yamada’s relationship from the perspective of Moeko, the follow-up on Ichikawa and Yamada’s double date, and the secret story of Yamada’s mother.

The publisher also hints at a possible story set ten years later.