While trust--who to trust, who not to trust, why be trusted, why not be trusted--is an important motif and theme throughout Wonderful Fool, including in Chapter 8, a more important theme and thematic question is what is the motivation behind Gaston's proclivity to trust and to accept being trusted. We don't learn definitively about what this motivation is until the end of the story when it is offered in terms of a flashback, but the thematic question is critical to driving the story on, even through Chapter 8.
To look at the story briefly from the beginning, Gaston--an anticlimactic descendent of the great Napoleon Bonaparte--contacts Takamori in Japan, who is an old school days penpal who resides in Japan. In garbled Japanese that Takamori and his elegant sister Tomoe have a difficult time deciphering, Gaston explains that he will be coming to Japan to visit them. While they do not have any idea of what Gaston wants, besides a visit, Gaston is clear and decided about it upon his best course of action.
Takamori and Tomoe are not favorably impressed with Gaston, especially as he has adopted a mangy, homeless dog and a prostitute friend. These actions are inconceivable to Takamori and Tomoe, who revile the lowest of the low classes. Things become even more inconceivable when a mistake about Gaston's identity leads him to being kidnapped. He will be held until the kidnappers have gotten revenge on someone who ruined their lives in the time of World War II. After Gaston delivers salvation through heroic and sacrificial actions, Takamori and Tomoe find out what truly motivated Gaston and what lay behind each and all of his bewildering choices: his compelling desire to be a Christian missionary.
Applying the end of the story backward to Chapter 8, you'll discover that Gaston's ultimate motivation was never very far below the surface of the action and psychological interactions there.
[Gaston is] bound to be written off as a fool. And so he is. But not just an ordinary fool. He is a wonderful fool. He is a wonderful fool who will never allow the little light which he sheds along man’s way to go out.