In Pulp Fiction, the motorcycle has multiple functions. Firstly, it serves as a means of transportation for the characters, allowing them to move quickly through the cityscape. Secondly, it is a visual element that helps to create the unique aesthetic of the movie. The sleek design of the motorcycle contrasts with the rough and tumble world of the characters. Moreover, it can be considered as a status symbol among the characters. Those who own or ride the motorcycle are often portrayed as having a certain level of bravado and independence.
I don't recall exactly which character rides the motorcycle in Pulp Fiction. There are so many characters and events in the movie that it's hard to pinpoint just one who rides it. It could be one of the minor characters or maybe it was just shown as a part of the scenery without a particular character being associated with it all the time.