Teresa of the Faint Smile, famed for her serene expression while effortlessly dispatching foes, stands as the pinnacle warrior of her era and is hailed as the mightiest Claymore ever. Her superiority in speed, strength, and agility over her peers is evident, yet her true prowess lies in an "unmatched sensitivity to Yoma aura." This ability lets her foresee adversaries' maneuvers with uncanny precision. Even when confronting Rosemary, a former top-ranked warrior turned Awakened Being, Teresa never needed to exert more than a tenth of her potential, which merely alters her eye color. During her training phase, she was labeled a "problem child" by her mentors.
At first, Teresa executes her duties with indifference toward those she aids, finding amusement in intimidating humans. This changes upon meeting Clare, a girl who starts trailing Teresa after being forsaken by her village. Initially annoyed, Teresa soon develops a fondness for Clare.
In an effort to offer Clare a semblance of normalcy, Teresa leaves her in a village. However, bandits raid the settlement, prompting Teresa's wrathful retaliation that results in their annihilation. This act breaches the Organization's cardinal rule against killing humans, making Teresa a target. Despite this, she spares fellow Claymores during their pursuit, influenced by her bond with Clare. Ultimately, Priscilla, pleading for death before awakening, catches Teresa off guard and slays her. Clare retrieves Teresa's severed head, persuading an Organization member to use it instead of a Yoma to transform her into a Claymore.
During Clare and Priscilla's climactic battle, Clare unleashes all her Yoki energy, reviving Teresa within Clare’s body. This resurgence enables Clare to vanquish the One-Horned Monster decisively. As Clare's form reverts to its usual state, she implores Teresa to remain, but Teresa reassures Clare that she will forever reside in her heart before they part ways.
