ドナ

DNA (Donna) is the name of the star in the universe. The giant city Megaro Dynamo is is inhabited by the two classes - titan (ruling class) and oak (laborers). The titans have excellent abilities, but their existence is endangered as they are cursed with reproductive function weakened with every generation. There is a girl from the titan class Mercedes who wished to undergo an experiment to fix this fatal trait. And the hero is an oak class member Cesare who wishes to protect her.

[From vndbreview]