Final answer:
Marty is discovering that there's more to Henry's childhood than previously known, with Henry being significantly influenced by his environment and family history. This discovery reveals the character's depth and complex past rather than superficial elements such as depression, knowledge about Japan, or sickness.
Step-by-step explanation:
Marty is discovering that there was more to Henry's childhood than Marty thought or knew about. The passages suggest that Henry has a deep connection and association with his surroundings, whether it's the influence of his family mansion or his dedication to study under restrictive conditions. Henry appears to be a person who bears the weight of his environment and circumstances, which have profoundly shaped his character and life choices.
From the text, we learn that Henry's mental condition is linked to superstitious beliefs surrounding his dwelling, hinting at a childhood filled with peculiarities that Marty was not aware of. It shows Henry as a character whose life and mentality have been deeply molded by the long sufferance of living in a particular location and dealing with family complexities. This context gives insight into Henry's personal history and reveals how his character has been shaped over the years.
In contrast to feeling depressed, knowing more about Japan, or having a serious sickness—none of which are supported by the provided information—the discovery about Henry's childhood is the element that best connects to the narrative given.