Haru wo Daiteita: Afterward

100 years later from that day...

Kato Ibuki, who abandoned the position of the elite Air Self-Defense Force Lieutenant and volunteered as a space pioneer of JASA, will take a 7-day selection test in a closed space.
While working on a task with Kaguya, an AI robot he met there, Katou came into contact with the feeling of "loneliness" in him and gradually became unable to leave it alone.

Also includes "Spare Key Requirements", telling from the perspective of Katou's nephew and actor Yousuke, who belongs to Iwaki's company.