This is the 4207th most frequent Swedish word.
seriens
"Seriens" means "the series' " (possessive form of "series" in Swedish).
In this sentence, 'seriens' functions as the possessive form of the word 'serien', meaning 'series'. It refers to something related to or belonging to the series.
Seriens huvudkaraktär är mycket intressant att följa.
The series' main character is very interesting to follow.
Here, 'seriens' again indicates possession, specifying that the episode discussed is the latest one belonging to the series.
Jag förstod inte slutet av seriens senaste avsnitt.
I did not understand the ending of the series' latest episode.
'Seriens' is used here to describe that the development being mentioned belongs to the series.