Essentially a 'paragon class' - as the ItCo series defines it - is a basic class not just specifically suited to the classic abilities of a particular race, but can, in fact, only be pursued by members of that particular race which it is crafted for. In this case, only Yaksha characters can take levels of Rakshasa Paragon and become full rakshasa in the process. Not even other evil outsiders or other similar entities can train in the class; only Yaksha. Now, each of the books in the series has a seperate paragon class for each race they cover. One for medusa. One for minotaur. One for wights, and so on. Nothing prevents the basic, 0th-lv. creatures presented in the books from pursuing standard classes, and most of the books contain at least a few racially-tailored archetypes for said standard classes as well. But only the race each book was designed about can take take book's paragon class.