Rideword

 is a monster that resembles a book and is usually found in magical libraries. It is unknown if they are a nuisance or a security measure.

Story
During the Magic Festival in Geffen, Iris is abducted by Sakray to lure Chaos to him. Their battle culminates within a secretive library within the Geffen Tower. While fighting, Chaos is accosted by a group of s and Sakray takes advantage of them to gain the upper hand.

Ragnarok Online
s make an appearance in RO as killable monsters. Unlike their manhwa incarnation, the in-game Ridewords feature primarily an eye icon on their cover rather than a variety of books. They're mainly found in the Glastheim dungeon.