Moto, Ochikobore Koushaku Reijou desu.

Claire Martino has a fairy-tale life anyone would envy, with a noble upbringing, a crown prince for a fiancé, and a promising future ahead of her as Noston's most powerful mage. That is, until everything crashes down around her when all of the family magical talent goes to her half sister, Charlotte, instead. With her engagement broken and reputation tarnished, Claire flees the only life she's ever known and sets off on an adventure to find the freedom she's craved all along. It's anything but easy, but fortunately for a girl with dignity, talent, and a whole lot of bravery, nothing is impossible...even turning out to be a video game character! Much to her surprise, Claire finds herself periodically teleported to modern-day Tokyo where Claire Martino is no more than a side character in the classic dating sim game Upstart: Eternal Love. Yet even that won't stop Claire from saving the day so she can unlock the good ending of her own route.

(Source: J-Novel Club)