Yoshiko's purpose in the novel The White Boy Shuffle is much more than just being a "mail order bride". She becomes a powerful companion to Gunnar by exposing him to Japanese literature and culture. Through this exposure, Gunnar develops a new, more complex view of his world. Further, Yoshiko's exposure to western culture (initially through Gunnar's poetry) and the English language have allowed her to develop a strong relationship with her new husband.
Upon meeting and getting married, Yoshiko defends herself against Betty and Veronica successfully, thus winning their approval as opposed to fighting with them outright. This display of confidence gives Gunnar and his family more confidence in their relationship. Gunnar's world seems to open up literally and figuratively the moment Yoshiko touches Gunnar's anus for the first time. The newlyweds are off to college together, a place full of possibility (even though we end up seeing Gunnar being pretty disappointed). After a hard day at class, he returns to his dorm butt naked and falls into Yoshiko's lap. Her response is very casual, revealing that their relationship has risen to a much greater level over the course of their time together.
What makes this scene interesting is how casual she remains throughout the bizarre events. Her behavior in part is what makes people uncomfortable with the novels course, as her apathy adds a sort of surrealism to the novel that people don't expect.
Yoshiko's behavior illuminates how comfortable she and Gunnar have become over the few weeks they've known each other. As mentioned in class, Yoshiko's constant butt poking is one of the many twists on stereotypes the novel presents. Typically, African American males are supposed to be extremely masculine, however this kind of behavior between Gunnar and his wife is emasculating him in a way that makes the stereotype not fit quite right.
By the end of the scene, with the help of his entire Writing 104 class, Yoshiko has convinced Gunnar to publish a book of poetry.
Yoshiko's most important influence may come from her letters to Gunnar while he's away playing basketball. She sends him traditional Japanese literature that creates a new perspective for Gunnar. Of course, the literature resonates with him because he's a nerd who loves to read, but it gives him an idea of what other philosophies there could be in the world. Eventually, the most relevant ideology he receives from Yoshiko is that suicide is not giving up, but a defiance against the enemy.
This idea drives the end of the novel, as countless people begin sending Gunnar death poems before the commit suicide, in haiku format. Japanese death poems were written by samurai before committing sepukku by cutting their abdomen and bleeding to death. It was considered honorable as opposed to pitiful.
Yoshiko provided Gunnar the information he needed to drive the movement, however when Gunnar believes it is time for him to commit suicide she is violently against the idea. She cries out that she knew Gunnar would leave her with a baby to care for on her own. Ironically, the only Japanese character in the novel is against the Japanese suicide method that is sweeping the nation! It is hard to say whether Yoshiko is against the idea of seppuku as a whole, or for her family in particular. But there is no doubt that Yoshiko played a pivotal role in the novel.