It is a limited-time event that challenges players to achieve consecutive wins in races. If you get three consecutive 1st-place wins, you become the Kart Pro. You'll add to your record when you finish in 1st place, and you can maintain your consecutive win record if you finish in 2nd or 3rd place. While not participating in a race, you can exit the event screen or quit the app and still maintain your consecutive win record.
Your consecutive win record will be reset if you get 4th place or below. The record will also be reset if during a race you tap Quit, quit the app entirely, or if there is a disconnection caused by a communication error.
Rewards can be checked on the Kart Pro challenge card. The reward for completing the entire Kart Pro challenge card varies depending on your grade when the event begins. In the case that the event period ends while you are still in a race, you would not be able to receive the reward for completing a challenge that would have been completed if the event was still active.