This is the 18073rd most frequent Russian word.
фэнтезийных
"Fantasy-related."
Here, 'фэнтезийных' acts as an adjective describing 'жанрах', specifying the type of genres, focusing on the fantasy aspect.
Я часто читаю книги, написанные в фэнтезийных жанрах.
I often read books written in fantasy genres.
'Фэнтезийных' is used as an adjective describing 'миров', referring to imaginative settings characteristic of the fantasy genre.
В художественном клубе обсуждали создание фэнтезийных миров.
In the art club, they discussed creating fantasy worlds.
In this case, 'фэнтезийных' modifies 'сюжетов', showcasing an association with narratives from the fantasy genre.