The Bunny is recommended to complete the only level as fast as possible; however, it is nearly impossible to lose unless you are trying, so any of the characters available in this tunnel can be used.
The following is a brief description of the story in Launch Site A. More information about the story can be found here.
After beating Launch Site A, a cutscene starts which stars the Duplicator and the Angel. The Duplicator asks if the Angel thinks he can get away with spoiling his son. The Duplicator mentions two times when the Angel solved the problem for the Child and asks what lesson the Angel is teaching to the Child. The Angel says he is teaching him how to solve problems but the Duplicator thinks the opposite. He says that his son will think that if he waits long enough someone will come and solve his problems for him. The Duplicator says that the Angel can't talk to his son and no more problem solving and give his son a chance to learn.