-Just retried, my memory was good :
There's 3 option for ML participants, then 3 option for ML structure. A bit complicated to explain but there's multiple choices; It's better to try yourself and check because it's complicated to explain 😅
1. If you select "Club of J-League" : the best option for that game, there's 3 choices, (1 isn't available for foreign clubs participants) : you can compete real J-League structure, or having an ML with others Euro league on it, or the same as PES with fantasy leagues, i'll explain the system after it's not like ML exactly (the closest to PES ML is the "Play in Euro League")
In brief for J-League clubs : 3 option of ML system. The old, the one without D2, and the J-League special ML.
2. If you select "Clubs of foreign country", you got 2 options, or "Play in Euro League" is the option to play with strict leagues and no D2 (even if you can put Anderlecht in La Liga) of 20 teams without promotion/relegation.
.... And the very special "Create an original league" is again ANOTHER system or ML : 20 teams in Division 1 and 14 in Division 2 / I just check and i'm WTF

It's the TOTAL FANTASY league in fact!
When you think how restricted we are since PES 2014 vs all those options... Sniff