Diagnosed with dementia, Yuriko's mind quickly begins to fade. Yet, for her son Izumi, memories of the mother feel as vivid as when he lived them. One in particular, when he believed she had disappeared, haunts him terribly.

Shun Fujishiro is a psychiatrist and works at a university hospital in Tokyo. He is engaged to Yayoi Sakamoto. One day in April, when he is about to marry Yayoi Sakamoto, he receives a letter from his first love Haru Iyoda. They dated 10 years ago. Suddenly, his fiancé Yayoi Sakamoto disappears.

A man gets lost in an underground passage. He follows the "guide" through the passage, but one after another, strange things happen to him. Is this space real? Or an illusion? Will the man be able to escape the passage?