At a "Cognitive Science Laboratory" in a small university somewhere.
Haruka Ninomiya, a recent university graduate student,It has been 1 year since she started working as an assistant under the "professor" who is rumored to be quiet and strange.
But he didn't tell her anything about the research theme.And she also spent her days in frustration with her clumsy relationships with professors.
One day. When she dozed off without doing anything in the lab as usual, an old server fan is spinning.
When she wakes up, she notices as if she is in a world something like white, shallow-water.It is the unconscious world which human beings have. The professor has been studying it for eight years.
It was a world made by LiDiA (Liquid Diving Assembly), a device for diving into the unconscious sea.
In the unconscious world, Haruka meets a mysterious orca that can speak language.
Then, to return to the original world, she goes to the sea with a killer whale to find the professor.
And there, she finds a mysterious incident that happened in the laboratory eight years ago, the big sins that the professor has, and the truth which he has confined to his own unconscious bottom.