"Step on a sha-dow, step on a sha-dow,
One shadow,
Two shadow,
Three shadow,
FOUR.
Back to one and keep your soul."

Kakeru and his girlfriend Yuu
are caught up in the investigation of the
unexplained death of a professor.

His final research was a strange nursery rhyme...

"Step on a sha-dow, step on a sha-dow..."

The shadows of everyone
in this case are disappearing.
Those who lose their shadows
die soon after.
Kakeru follows the mystery to its base truth...
and what he finds is horrifying.

[From DLsite English]