A meteorite crash has brought a mysterious monster known as Acrylamide into the world, threatening humanity. The only force capable of fighting these creatures is a magical girl. Akuto is a young man whose older sister, Shiin, is one of those magical girls, fighting under the name Shiny. He has always supported her efforts from the sidelines. However, after a fateful battle, Shiin defeats an Acrylamide but then takes her own life.

Driven by desperation and a deep sense of loss, Akuto finds a way to travel back in time to before his sister ever became a magical girl. His goal is singular and direct: to change the future and prevent her tragic death. But his actions put him on a path that challenges the very system that creates magical girls. The story follows his time-traveling mission to save his sister, exploring the dark side of the magical girl system that demands such a heavy price from its heroes. The complete manga is a three-volume series that blends action with a story of familial devotion and time travel.