Atsushi Fujii serves as the childhood friend of protagonist Shoma Mihara. Close during elementary school, the two lost contact before high school. Atsushi initiates the story by sending Shoma a message via a mobile application, inviting him to a reunion party at a remote festival site hidden in the wilderness. This invitation prompts Shoma's journey to the secluded Tanabata festival location.

Throughout the festival preparations and ceremonies, Shoma gradually uncovers the truth behind Atsushi's absence. Contrary to Shoma's belief or repression that Atsushi simply moved away, it is revealed Atsushi actually died. This repressed memory surfaces for Shoma during the festival's climactic moments.

Atsushi's role culminates within an artificial intelligence-generated simulation during the festival ceremony. This simulation enables Shoma to visually and interactively confront Atsushi's absence, facilitating a final opportunity for acknowledgment and farewell. The mechanism enabling this encounter, including the initial invitation, is linked to the mobile application that delivered Atsushi's message.

The festival's purpose is implicitly connected to enabling participants to reunite with deceased individuals important to them. Atsushi functions as the specific figure enabling Shoma's emotional resolution within this framework. His background prior to death, including circumstances or causes, remains undetailed.