The protagonist is the System, not a person, though it can turn into one.
A loser gets a System and becomes a winner in life. The goddess he seduced and then abandoned was only a stepping stone for him. Only after she was betrayed, heartbroken, and took her own life does the System realize she was the one it had once wronged.
After being reborn, the System does everything it can to stop the loser from succeeding and seducing the goddess, and tries to seduce her itself.
Basically, it's one of those harem stories where the System is reborn and stops the loser from succeeding, then seduces the goddess itself.
