Akuyaku Reijou Level 99: Watashi wa Ura-Boss desu ga Maou dewa Arimasen

Yumiella Dolkness is your run-of-the-mill villainess in an otome RPG—except for the fact that she's also secretly the overpowered hidden boss. But Yumiella wasn't always Yumiella, you see. In her past life, she was nothing more than an introverted college student and devout gamer. So when she realizes that she's been reincarnated as a hidden boss, she's determined to steer clear of the protagonists and avoid her demise at their hands. All she wants is a nice, quiet life. Too bad when her gamer instincts kick in, Yumiella can't just ignore her awesome stats... A girl's gotta grind! So, with plenty of time on her hands before starting life at the academy, she gets a little carried away and maxes out her level at 99. And when everyone else finds out, they get the wrong idea about her power—now they think she's the Demon Lord! Is this OP villainess strong enough to win back the peaceful life she always wanted?! (Source: J-Novel Club)