In the movie, GoGo and Wasabi are good friends and fellow students at the San Fransokyo Institute of Technology. Despite this, however, they seem to be polar opposites: GoGo is an adrenaline junkie with a rough attitude, while Wasabi is more neurotic, and is obsessed with following the rules. Their personalities are seen bouncing off of each other several times in the film, such as when GoGo takes one of Wasabi's tools without permission, messing up his organized desk and causing him to freak out. The most famous example of their dynamic is during the car chase scene: Wasabi is obsessed with obeying all traffic rules (including stopping at red lights) while being chased by Yokai, causing GoGo to snap and take the wheel from him by force. She then drives the car a lightning speed through the city, while Wasabi is absolutely terrified.
Fans of the ship seem to like this "opposites attract" dynamic, and often portray Wasabi and GoGo as the bickering couple who love each other nonetheless. Fans also believe that their personalities would eventually rub off on each other, causing each one to be more complete.
Note: Please add only ones that are part of the RotBTD fandom