9th letter is M or 9 letters in length
M4 might mean the fourth letter is M or 4th word starts with M
<4 could mean it’s less than four words
and the 1 might mean the season number :p

If it’s a series that starts airing in the next season then you just have to look at all the names that contain the letters posted to far “OSASI”, then look at stuff like number of vowels, words, letters, if you think the code represents the name of the show. Otherwise it could mean virtually anything to background info, actors, air date, manga etc

I highly doubt it’s incredibly complicated, it’s just that without some kind of key it just looks like a bunch of useless numbers to most people. And I can’t be stuff going any further than this :p