MOND-018 Aunt turned into an appreciation doll

A young man receives a letter from his grandfather when he was a child. The sender was the young man’s aunt, the daughter of his grandfather’s mistress, and a woman who was close in age and called his sister. The content was that my grandfather passed away, so I should go back to my hometown. The sight that the young man, who made up his mind to return home, witnessed at his parents’ house was unbelievable… What is the truth that the young man witnessed?