The game will be dedicated to the son (player), who returns home as an exchange student. It was his last year at school, and he returned home to find work.
When he comes home, he notices that some things have changed, in a bad way. His mother, his stepfather and his two sisters (younger and older) live at home. His stepfather was always a good person, and you, and your family, accepted him as a dad.
What has changed, and why this "may be bad" will be shown in the demo version of the game.
The game will be the player's choice as to what content will appear. The player can choose who the romance will be with if he wants to start an affair with a family member, and so on. He will choose how he wants to do this, start a romantic love story or be an asshole who takes everything he wants or corrupts them to make money (blackmail).
Thus, the player decides what he wants to do and how he wants to play. Like a dating simulator. But this game will have a dark and violent background. The game has rivals who want to "steal" your girls; etc.