Mme. Yoshoto is most notable in the story for cooking fish breakfast, offering Jean eggs, and for worrying that Jean needs a chair in his room. Because Jean sees her in the same stereotypical light as he does her husband, she is "inscrutable" to him, even though he tries to make us believe he's an expert on the physical appearances of Asian people by telling us that she looks "rather more Malayan than Japanese" (23).
At the same time, it's clear that Jean feels genuine affection for both of the Yoshotos. He wants to connect to them, but doesn't know how. When he hears the moaning in the night he imagines that whichever Yoshoto is responsible for the moaning will tell him all about the problem, and thereby be relieved of suffering. We think of them as his temporary, substitute parents and his temporary partners in exile.