Teresa

Teresa was the strongest Claymore of all time. She was famously known as Teresa of the Faint Smile for effortlessly slaying enemies with a faint smile on her face. She is so powerful that she rarely, if ever, has to use even 10% of her Yoki in battle. Her rise to Claymore No. 1 leads to the demotion of the previous No. 1, Rosemary, who, angered by Teresa's promotion, challenges her to a duel as an Awakened Being. Not long into the fight, Teresa dispatches her easily by releasing only a little of her Yoma energy.

Early Life
Before becoming a Claymore, she was referred to as a "problem child" by her handlers during her training. In one of her escapades, she ran into Rafaela.

As a Claymore, Teresa is a cold-blooded killer who cares for no one, only helping villages because she is ordered to, and taking pleasure in scaring humans. She is also solitary and rarely has contact with any of the other Claymores in the organization (she was surprised when Rosemary sent her a Black Card).She also keeps secrets from her handlers ,and severely distrusts the Organization.

Time with Clare
This changes when Teresa saves a young girl who had been kept as a prisoner and toy of a Yoma. The girl then follows her on her journeys. She is initially extremely irritated by this girl tagging along wherever she goes, but eventually grows fond of her. Teresa gives the girl the name Clare, after the twin goddesses, Teresa and Clare. Clare awakens Teresa's lost compassion, leading Teresa to say:

"This young girl, whose small body is only half the size of mine, taught me that, tears can, too, flow from these silver eyes"

From this point onwards, Teresa openly shows her affection on Clare without holding back her emotions (buying her clothes and allowing her to sleep on her lap), but eventually, she leaves Clare in a village, believing that a normal life with humans would still be better for her. However, the village is soon raided by bandits and Teresa rushes back to save her. Seeing Clare's bloodied form, Teresa flies into a rage and kills the bandits, breaking the rule that a Claymore should never kill humans, no matter what the circumstances.

Battle with Priscila
Because she killed humans, the Claymore organization marks her for death. It dispatches a team of five Claymores of unknown ranks to execute her. Teresa cuts down but does not kill the Claymores, stating that Clare had become her reason to live.

Claymores No.2 to No.5, Priscilla, Irene, Noel, and Sophia, are then assembled to kill her. However, Teresa defeats them all without even releasing her Yoma power. She intentionally spares the lives of Claymores No.3 to No.5, but considered killing Priscilla because she senses that she was the only Claymore with the potential to surpass her in combat. But her relationship with Clare had mellowed her, and she ultimately decides to let Priscilla live. Teresa leaves the town with Clare, leaving her former comrades wounded. However, Priscilla pursues and attacks her in blind rage. In her anger, Priscilla accidentally releases too much Yoma power and nearly Awakens, but Teresa defeats Priscilla again while releasing only 10% of her power. Priscilla then cries and begs Teresa to give her a merciful death before she fully Awakens, but as soon as Teresa drops her guard, Priscilla picks up the sword, attacks and decapitates her. Teresa's severed head is taken by Clare who carries it until she finds a member of the Organization. She begs him to place Teresa's remains inside her own body, becoming a Claymore in order to exact revenge against her savior's killer.

Power and abilities
According to Irene, Teresa is called "Teresa of the Faint Smile" because her smile is her only visible asset. Though she excelled in speed, strength, and agility, the other top Claymores supposedly exceeded her abilities in those areas. This is later proven false as Irene later states the she had underestimated Teresa's power. What made Teresa so powerful was her "unparalleled ability to sense Yoma aura" (Yoki). Whenever Yoma or Claymores move, they emit demon energy to the parts of their bodies they're about to move. Though any Claymore is able to sense Yoma energy, only Teresa is able to sense it accurately enough to predict her opponent's moves in battle. She also has an extremely high amount of Yoma energy in her body. In the moments before Priscilla awakens, Teresa is strong enough to repel her attacks with just enough Yoki for her eyes to change color (10% release), as well as defeating the former No. 1, Rosemary, who had awakened,(which probably put her in the same power level as an abyssal one), with no problem at all using the same amount of power. Throughout the series Teresa has been referred to as the most powerful No.1 in history.