The Divine Child of Past and Present Lives

The male protagonist and his younger sister depend on each other in a life of hardship. His ordinary high school life changes when he meets the heroine and recalls memories his sister was supposed to have sealed away. In their previous lives, the three met in a laboratory, where they were young children transformed into inhuman "divine children." What will the awakened protagonist do? Will the three of them find happiness in this life? What awaits him up ahead?