Cattleya Yvette la Baume le Blanc de la Fontaine serves as the middle sister between Louise and Éléonore de la Vallière. She possesses waist-length pink hair, red eyes, and stands 171 cm tall with measurements of 94–63–95. A chronic illness renders her physically frail and sickly, preventing marriage despite her 24 years. Out of compassion, her father allocated part of the Vallière inheritance to establish her as head of the separate House of La Fontaine, where she remains the sole member.

Gentle and optimistic, Cattleya harbors deep affection for Louise, recognizing her sister’s potential and unspoken romantic feelings for Saito before others. She supports their relationship regardless of Saito’s commoner status. Demonstrating loyalty, she aids Louise’s escape from the Vallière estate using earth magic to manipulate a golem and lift a drawbridge. Later, she temporarily teaches at Tristain Academy of Magic to support Louise, accompanied by her pet animals.

As a Triangle-class earth mage with a cat familiar, Cattleya summons earth golems for combat and utility—such as halting a thief during an incident where stolen Rubies of Wind and Water were falsely pinned on her via rings planted under her mattress. She also exhibits water magic affinity, conjuring water spirits to heal Saito’s severe injuries.

Despite her fragility, Cattleya volunteers alongside Éléonore as a hostage during Menvil’s academy attack to secure other students’ release. She participates in key family events, including Louise and Saito’s wedding.