“Bye-bye, my precious and most beloved person.” On the way home from school, Sakuya and a group of friends stop by a shopping building that unexpectedly collapses. Sakuya, the quiet and unsociable protagonist, ends up dying instead, protecting the life of her best friend, Otoha. “Another world…..No way….” When she wakes up, she finds herself in an unfamiliar labyrinth with a dangerous creature with a big mouth looming over her. She wants to escape, but she can’t move her body. To the impatient Sakuya, the smartphone, one of the seven tools, tells her the truth in an indifferent tone. “That’s because Sakuya-sama is an infant.” “….Haa?!” And so, Sakuya was forced to live in the Great Labyrinth. There, she learns the truth of the world and the danger that looms over her. For the sake of her best friend who lives in another world, Sakuya begins to move again, but――