If you have always wanted to invite a friend and have yet to notice this event going on, its time to take advantage of the free permanent access account.
For limited time only, hurry before it runs out.
This video details how to go about getting the account as well as how to effectively level up your character quickly to fulfill the leveling condition.
Just to add on:
The last Permanent access will be distributed on February 12, 2020 at 12:00. If you received the 14-day guest pass coupon during the event period, you will still receive permanent access even if the event has ended as long as you complete missions 1 and 2 during the coupon validity period. (Example: If you received the 14-day guest pass coupon on February 4, 2020 (Tue), then you can achieve the missions 1 and 2 until February 11, 2020 (Wed) to receive permanent access on February 12 (Thu) at 12:00)