Atonement for my stepmother: an incest relationship that abolishes sins to my son

Yui is a widow who lost her husband in an accident when she was newlywed and ends up living with her stepchild, Shota. Shota, who spends time supporting his broken-hearted stepmother, is unable to contain the lust that creeps up in front of the memorial photograph late at night, comforting Yui, who is coquering him, and forces him... Due to loneliness, Yui also accepts her desires and begins a twisted newlywed life. However, such a life could not have been successful, and the end suddenly came. One day, Shota finds a letter written by Yui to his father from his father's altar. What was written there...