The answer is 10 online games in each individual sport to unlock its certified pro (which unlocks its pro league ranking for your player). You do not need to win, just playing unlocks them.
Ex. Play Tennis 10 times (doesn’t have to be consecutive) online will unlock Tennis Pro League
Ex. Play Bowling 10 times will unlock Bowling Tennis Pro League, and the same for Badminton, Bowling, Soccer, Chambara, and Volleyball.
That’s it. Have fun, you will start off at E Rank.
When you see this, you unlocked Pro League!
PS: There is no 2 Player Pro League. (I just tried it out on April 29, 2022)
