Lephie is a descendant of the Great Hero Persey, who fought in the Sealing War that banished the Magicant people to the Sealed World (and eventually caused them to end up in Medlia). She has inherited the Holy Blood from her ancestry, meaning that she could unlock and wield Persey's magic artifacts if she found them. She grew up in a well-to-do family, and eventually was chosen to be a retainer for Princess Falana of Fezelia. However, she feels her childhood was largely defined by either being sucked up to or teased because of her ancestry. Persey was considered something of a rogue priest, and his legacy left some with a bad taste in their mouth even hundreds of years later.

When Lephie is introduced, she's a quiet, bookish sort with a passion for researching the world's history. With the help of Fenne, one of two humans that ended up in the Sealed World with the Magicants, she ends up uncovering Fezelia's biggest secret: Project Y'tiar. This project was the use of the royal family of Fezelia in a "breeding project" to eventually produce a suitable vessel for Y'tiar, a dark god promising power and dominion for whoever could be responsible for his incarnation. She is eventually involved in the final showdown with a possessed Falana, though she takes a more passive role in the fight than her friend Arilee.

At the time of her arc, she has stepped down as a royal retainer and has moved to Medlia with Arilee, looking to experience what Lemanta lost in the Sealing War for herself. She remains thoroughly disgusted with the truth behind Fezelia and, by extension, the Sealing War that the country started. She eventually falls in love with a Caprimet and effectively rebels against her ancestor's tenets.