What kind of title is this?: Manga.
Where can I read it?: Reading links are listed for Pixiv Comic, Official Site. Check availability in your region.

Synopsis

About Villainess Level 99: I May Be the Hidden Boss But I'm Not the Demon Lord

A college student finds herself resurrected as Eumiella, an evil daughter of the nobility in the world of an Otome RPG that she played in her previous life. In the RPG, Eumiella isn’t worth thinking about at first, but in the endgame content she returns as a hidden boss, complete with ridiculous stats that put her on par with even the game’s heroes. After being essentially abandoned by her parents at their family domain, the flames of Eumiella’s former gamer soul are ignited, and she takes to leveling, and leveling, and leveling, until...at the time of enrolling in the Royal Academy, she discovers that she is level 99. Though she’d originally planned to live a peaceful and discreet life, the game’s heroine and her love interests suspect that Eumiella is in fact the infamous Demon Lord. These ridiculous powers invite all manner of trials and tribulations. So begins the fantasy tale of a most powerful, evil hidden boss (who wishes she could just live a life of peace and quiet). (Source: One Peace Books)

Comedy Fantasy Romance