Echo is a character from the manga Pandora Hearts. She is introduced as a young girl who serves as the personal attendant to Vincent Nightray, carrying out his orders with unwavering precision. She has a small, slender build with short silver hair and grey-blue eyes, typically dressed in a blue and white outfit with wide sleeves that conceal her weapons. She refers to herself as being sixteen years old.

Her true nature is complex. Echo is not an ordinary human but a constructed personality known as Duldum, created by the powerful Chain named Duldee. Duldee created this artificial persona to protect the mind of its contractor, a Baskerville girl whose original name is lost but who later goes by the name Noise or Zwei. The contract with Duldee was so traumatic that it fractured Noise’s psyche, and Duldee created Echo to act as a shell, allowing Noise’s true consciousness to sleep safely within their shared body. Echo is, in essence, an echo of the original person, a disposable personality intended to absorb the damage and preserve the core self. Many such personalities had been created and had faded away before her, making her the longest-lasting and final version.

In her daily life, Echo presents as a model and emotionless servant. She is a classic example of a character with limited emotional expression, speaking in a consistently polite and formal tone. She moves and acts with mechanical efficiency, following Vincent's commands without question, a trait that leads others to perceive her as a doll or a puppet. However, this lack of outward emotion belies an internal world. She privately finds Vincent to be annoying, particularly due to his messy habits and volatile moods, though she feels she has no right to refuse any treatment he subjects her to. She keeps a diary where she records her observations by the minute, a practice born from her need to document the proof of her own transient existence. Her internal landscape becomes more defined following her interactions with the protagonist, Oz Vessalius.

Echo's primary role in the story is two-fold. On the surface, she is a formidable operative for Vincent, using her agility and skill with concealed twin short swords to capture targets and eliminate threats. Her true, deeper role is as the guardian of Noise’s heart. Her actions and her very existence are all directed toward this purpose, even as she serves as Vincent’s attendant to allow Noise to remain close to him. Her personal journey becomes one of questioning her own predetermined purpose and moving from being a simple tool to an individual with her own will.

Her development is almost entirely catalyzed by her relationship with Oz Vessalius. When they first meet, she finds him to be a nuisance, but his words and actions slowly affect her. He treats her as a person, and during the St. Bridget's Day festival, he shows her what fun and happiness feel like for the first time. A running gag in their relationship is Oz calling her by the nickname "Echo-chan," which she always immediately corrects with "It's Echo." This correction becomes symbolic of her asserting her own identity. A pivotal moment of her growth comes when, inspired by Oz's words, she disobeys Vincent by retrieving an antidote needed to save a girl named Sharon, directly defying her master's orders. This act demonstrates the emergence of her own sense of right and wrong.

Her internal conflict culminates in a confrontation with Duldee and Noise. As Noise's mental state deteriorates further, Duldee attempts to take over their shared body. In this final battle, Echo uses the sense of self she has developed to rebel against her own creator. She reaffirms her purpose not as a disposable tool, but as the mirror and echo meant to protect and restore Noise's true heart. She successfully awakens Noise's suppressed memories and feelings, allowing her to remember her genuine wish to protect Vincent.

Echo’s most significant relationships are with the two personalities sharing her body and the two people who define her existence. She is antagonistic towards the aggressive and possessive Noise, yet her core function is to care for and protect her. Her relationship with Vincent is one of complete subservience on the surface, but she privately finds him annoying and her growing will leads her to defy him. Her bond with Oz is the most transformative, as he is the one who validates her personhood and awakens her capacity for joy and independent action. There are subtle hints of romantic affection from Echo toward Oz, who treats her with consistent kindness.

In terms of notable abilities, Echo is a highly skilled combatant. She hides twin short swords in the sleeves of her uniform and wields them with ambidextrous proficiency, using acrobatic movements in battle. As a derivative of a Baskerville, she possesses enhanced endurance, speed, and strength beyond that of a normal human, and can heal from wounds at an accelerated rate. Her most unique ability is her very nature as Duldum, allowing her to take control of her shared body and, most importantly, to collect and safeguard the broken fragments of Noise’s heart, keeping them safe until they can be restored. This maintenance of the heart is her most sacred and fundamental duty.

In the end, after restoring Noise’s true heart, Echo accepts the conclusion of her own existence. With her purpose fulfilled, she thanks Oz for giving her a sense of self and disappears in a shower of ash, having finally fully become her own person.