From Main Menu, select 'Game Mode' and then 'Event Mode' > 'Create Event', choose difficulty, 'Beginner' being the easiest, name the event, choose the type and make sure you set the number of fights to 8, then press 'Continue'. You can edit the fight cards, but you can also press (Finished) to accept the preselected card and proceed.
When the event starts, you can choose the side you want to play with or let the CPU battle it out for you, but don't choose 'Skip Fight' ever, view or play all 8 fights and it should unock when the event is over.
The fastest way for getting this is selecting the 'beginner' difficulty and go for the knockout. It only takes 2-3 minutes per fight to complete a fight.