Ushikawa, in full Toshiharu Ushikawa (although he is usually only referenced as Ushikawa) is a primary character in Haruki Murakami's novel 1Q84. His name literally translates as "River Bull" (a name that may be a comment on his ungraceful demeanor). Like the other two main chracters, Aomame and Tengo, portions of the book are shown from his point of view. Unlike them, he is an antagonist, a generally unsympathetic character, and is introduced much later in the book. In Japan, the three sections of the book were published separately, and he does not become a narrative character until the third part of the book.
Ushikawa is a private investigator hired by a religious cult to investigate and intimidate the book's two main protagonists. His major feature is an incredible ugliness, which manifests both in his physical appearance and in his dress, which is tacky and mismatched. Despite his physical unattractiveness and lack of tact and manners, he is quite skilled as a private investigator, having a thorough sense of detail and a creative ability to gather and link information. For these reasons, he is retained by the religious cult as an investigator, and comes very close to finding out about Tengo and Aomame.
The characterization and development of Ushikawa is, I think, tied up very closely with the thematic development of the novel as a whole. It is possible that Ushikawa is just introduced as a way to move the plot forward and to provide information to the reader. But given the effort that Murakami put into this book, I think that there is more to it than that.
Near the conclusion of the book (and everything past here counts as spoilers), Ushikawa is tortured and murdered by Tamaru, a character who is on the side of the protagonists, but is methodically ruthless. While Ushikawa does have questionable morals, and is working for a religious cult that is trying to capture and kill Aomame, he is also not shown as being prone to or fond of violence on a personal level. And since we learn at least a little of Ushikawa's lifestory, there is reason to be sympathetic for him. For me, his cold blooded murder, occurring near the end of the novel, was a confusing and visceral surprise.
In addition, before his death, Ushikawa becomes one of the novel's few characters able to see that there are two moons in the sky, meaning he has reached some level of insight about the enigmas that surround the book. I think that despite his ugly appearance, ethical shortcomings, and late introduction to the novel, Ushikawa is meant to be seen as a major character. I also think that his murder is meant to bring up issues of morality in the reader, because while he is an antagonist, his violent murder by a character who we were previously sympathetic to brings up issues of violence and morality that are important to the books central plot and theme.