Description

The deterioration of environment conditions increases water coverage drastically leaving little space for humanity to occupy. A new “synthesis” technology resembling magic is developed to restore the former prowess. The spread of this tech is accompanied by the revival of "Tenma" legend as it's the power that can be used for for angel and devil purposes.
Main character is one of those adults who start to consider "Tenma" legend as a fairy-tale. One night he discovers a mysterious spring. Four girls wait for his there.

[From vndbreview]